Soap was not one of those things.
There’s this persistent myth that people in the Middle ages didn’t bathe. This is pure crap. They bathed, and they made soap. They had entire guilds for that purpose.
If nothing else, they used a lot of wool cloth, and soap is used there along with fuller’s earth to clean fleeces.
But you have to admit they don’t use it today in France.
Only 1 in five 
It’s all in how you market your new soap:
But not because it’s too expensive. Soap was common and affordable in medieval times. It’s not hard to make with ingredients they used all the time.
Actually, if you believe the Daily Mail, it’s the English who are a bunch of dirty buggers.
Limiting myself to the OP’s proposed situation of what I have in my household right now (rather than most of the later posters, where planning and a serious shopping trip would probably be necessary) nothing is particularly valuable. Nothing you are likely to have would be particularly valuable either.
The best bets have already been posted: spices, dyes, and some metal objects.
Little of our workmanship would be exceptional. Most people’s kitchen knives, for example, are crap; poorly balanced and shaped, and blunt with poor edge holding ability. The only novelty value in typical stainless steel knives would be in the metallurgy, and since you couldn’t teach anyone how to make it, or even how to work it into a different form (most stainless alloys crack at low forging temperatures, and people used to forging carbon steel wouldn’t know when they were at the right temperature for forging), it wouldn’t be worth all that much. And even high-quality kitchen knives would look appallingly plain to medieval eyes.
A cast-iron pan wouldn’t be valuable, or even remarkable. Medieval dishes weren’t all simple. Some were nearly as elaborate as modern ones. A medieval kitchen had dozens of implements you probably wouldn’t even recognize, some of it with better workmanship in some respects than modern pieces. Metal cookware dates back to the Greeks and Romans. Then it would have been valuable, just because iron itself was relatively difficult to obtain. Most metal cookware was made out of bronze at that time.
Most of the value in our possessions is their utility and desirability within our society. There are very few things of actual intrinsic worth, and even fewer with a use in a medieval society. Anything that requires resupply or repair to work is useless. Anything that requires social structures and precursor technologies is of very limited value because it would take literally decades to bootstrap — and that’s making the enormous assumption you could convince anyone at all to help you, because you’re damn-sure not going to be building everything yourself from scratch.
Frankowski cheated, and he wasn’t shy about it. There are scenes where it is made clear that a future descendent of his made sure that Conrad’s horse was a genetically engineered wonder, his sword was made with future metallurgy, he “just happened” to have helpful seeds, and some of the “chance encounters” at the beginning of the first novel were set up.
The books do realistically depict the kinds of problems someone would have in trying to prematurely advance technology, like having no lumber as we would think of it. They’d go out and chop down a tree, then take it apart into pieces as they needed it. There was no standardization. Everything was a custom piece.
He also did a pretty decent job of showing how feudalism would affect a time-traveling engineer. You’d need a sympathetic and extremely tolerant lord to protect your ignorant ass long enough to keep you from getting your head chopped off and shoved up it. That’s just for starters. You’d also need lots and lots of funding to start building the things you needed to work on more projects.
Guilds had vested interests in the market. They worked like a combination of a cartel, controlling prices, and de facto regulators, collecting fees from guildsmen and charging for approval of some finished goods as a guarantee of quality (or at least the payment of inspection fees). If I remember right, Frankowski had some guild guys actually try to kill Conrad at one point, which sounds about right.
I have my Bascinet and sword in arm’s reach, actually…
Armour and weapons were always valued.
Hey, I really do have a few cups of cloves, cinnamon, turmeric, peppercorns, allspice and several other spices in the cupboard, and half a cup to a cup of saffron, nutmeg, and some other spices that I use in smaller quantities. We do a lot of Indian cooking, and a fair amount of baking and cider mulling. I also have a set of rainbow colors of RIT dye in the basement that I used for one project. And a lot of fine sewing needles, and quite a lot of good-quality knives and scissors.
I also liked the idea of ziplock bags. Keep your valuables safe from water.
This is why I still say that knowledge is the most valuable thing you have. A good recipe for soap, (Though you might have trouble convincing anyone to use it - even in the last century, some people were convinced that it made them weak); a good simple way to convert reciprocating to rotary motion (a lathe for example); a cheap, simple way to make paper.
I am sure that once you arrived, you would be able to see many ways that tools and equipment could be improved, without going so far ahead that you would arouse enmity and suspicion. You might not get instantly wealthy, but if you could impress the right people enough, you might get a wealthy patron, which could be just as good.
You would probably do well to take all the medication you could lay your hands on for personal use.
Exactly, Bob++. Which is why I think a book of knitting and crochet patterns and stitches is so valuable. The tools are relatively easy to make, although a lathe would help. Nalbinding was the technique at that point; knitting is not a lightning jump away. Basic crochet is applied common sense. You have sheep, now you have practical fabric.
Didn’t you guys learn anything from Marty McFly?!
The answer is almanac 
I personally would wear out my printer and about 500 ink cartridges to print the entirety of the wikipedia site, make it my personal tome of knowledge and rule the world! 
One other thought to run up the flagpole and see who salutes; modern drugs have been mentioned before, but which one would be most valuable once you could prove what it did? A few thoughts on things that you likely have in your home right now, paracetamol, aspirin or an antiseptic cream that you could market as a salve.
One thing about “getting rich” via time travel. You have to take goods that are cheap in 2014 America but expensive/nonexistent in 1325 Europe, and exchange them for goods that are cheap in 1325 Europe but expensive/nonexistent in 2014 America.
Sure, you can sell your plastic bags and t-shirts for gold, but gold wasn’t cheap in 1325 Europe. A fantastic fortune in gold in 1325 Europe would be a small nest egg in 2014 America.
If you could bring back breeding stock for moas, dodos, thylacines, steller’s sea cows, passenger pigeons, quaggas, or great auks, those would be priceless. There are some European subspecies of animals that are now extinct in Europe that were around then, but these were very rare already. Bringing back aurochs is probably your best bet.
I didn’t see anything in the OP about being able to return, much less toting a great big cow. :dubious:
I don’t have any single item in my home that would be particularly valuable in medieval Europe, but I have a number of small-ish items that could help me establish myself tolerably well:
As many have mentioned, a vast array of textiles and sewing implements that would be luxurious by the standards of the time - Cards of sewing needles, a bolt of good upholstery fabric, several sets of curtains (brocades, sheers, even simple cotton/poly curtains - the ones in my girls’ bedroom and playroom are rich purple, pink, and blue, and would be rather valuable based on the color alone, if I understand medieval dye technology correctly.) Also, gobs and gobs of sheets - the high thread count cottons would certainly qualify as a luxury good at the time, and be suitable for very high-end undergarments for a noble. Even the cheaper sheets would be novel, in that they are relatively wrinkle-free and sturdy, and many have patterns. Plus, the handful of silk scarves I own, and maybe a couple of my formal dresses would be valuable for their material (brocade, velvet, satin.)
My ice cream churn has a hand crank. Ice cream wasn’t really introduced to most of Europe by that time, but all of the ingredients were quite available, as was ice and salt. I could be Ice Cream Maker to the King, with plenty of kitchen boys to turn the crank!
As mentioned by others - spices. I don’t have enough to make myself rich, by any stretch of the imagination, but enough to trade for some basic subsistence items to help establish myself. (Although I might have to keep my vanilla and cocoa to myself, and well-guarded, if I’m gonna be the official Ben & Jerry to the King! No way to replenish that supply for a couple of centuries past the time period we’re discussing. Ditto for my supply of “exotic” dried fruits - pineapple and cranberries and coconut and such. If I were planning ahead for this adventure, and the rules of this thought experiment allows it, I’d go buy a crapton more vanilla, cocoa, etc. I wouldn’t really worry about cane sugar, though, since adequate substitutes existed then.)
Kitchen knives and various household knives - I have good kitchen knives. Those are expensive now, and the quality would have been recognizable then, too. I’d likely keep at least a couple for myself (chef’s knife, paring knife, good pocket knife,) though, if this is a situation where I’m required to remain in that time. Really good pocket knives would have been valuable, I think, although I might have to “invent” the pocket! (I know, people typically used pouches, probably because of the high cost of textiles, if I’m guessing - no need to replicate the same thing on each garment.)
I’d definitely take sturdy shoes, but those would be for personal use. Everything I think I know about medieval shoe technology makes me think I wouldn’t find most very comfortable or practical.
Hosiery - imagine a 14th century lady’s reaction to nylon panty hose or tights!
Medical supplies - Thanks to my husband’s recent medical history, I have a ton of stuff in my Zombie Apocalypse medical bag. Broad-spectrum antibiotics, powerful anti-inflammatories, opioid pain medicines, etc. Plus common “modern miracles,” like aspirin and antibiotic ointment. Hell, I have a first aid kit that’s suitable for minor surgery! If the Ice Cream Maker to the King thing didn’t work out, I could set myself up as a doctor, at least until my supplies ran out. I’d take my first aid books, too, but those would also be for personal use. And if time allowed, I’d get every vaccination available to me in modern times, including (especially) smallpox, if at all possible. And I’d get my stepbrother to write me as many prescriptions as possible for basic antibiotics and get them filled ASAP. Most of those would be reserved for myself, but for the right price, I might save a wealthy nobleman’s son from an ear infection or something…
There are also about a dozen pairs of reading glasses floating around the house - those would have been the newest technology in Europe at the time, and certainly worth a bit to the right buyer.
I also have a bit of silver - trays and bowls and pitchers and flatware. No argument that those would be worth carrying.
And, thanks to having kids in school, I have a metric buttload of notebook paper, ballpoint pens, pencils, crayons, felt tip pens, etc. Sell that stuff to the local monastery, along with a couple of books I have on hand - nothing in modern English, but a bound, printed copy of Galen or the Koran or the Septuagint would be terrifically valuable, and out of the price range of anyone except the wealthiest noble or monastery. I also love the look of maps, and I think I have a reproduction of a couple of 18th century maps of Europe, Africa, and Asia. They aren’t accurate, but they’re better than four centuries earlier, and would be worth a few pennies to a military leader.
Thanks to our recent home remodel, I also have some quite portable and common items from today that would be expensive then - nails and hinges and screws, good chisels and hammers, etc.
Jewelry, of course. I don’t have any major stones, but fine gold or silver chains, semi-precious stones, and even costume jewelry would find a market, if only for the novelty of the workmanship.
Seeds: I have several packets of them - tomatoes or maize would be quite the novelty, and watermelons had only just been introduced to Europe by the early 14th century, although I assume they might have to be cultivated in a greenhouse in England. With enough lead time, that 10-pound bag of potatoes in the pantry might become enough seed to help alleviate the oncoming famine, or maybe just keep myself or my village fed. That bag of green peanuts I have for boiling might also serve the same purpose, but cultivation would probably have been very difficult in England - Spain seems more likely to have the right soil and climate conditions. Considering their nutritional value and the use of the tops to feed livestock, though, they’d certainly help during famine conditions.
Even something as cheap and simple today as the dozens of drinking glasses and glass kitchen implements in my cabinets would be very rare and valuable in 1310 England, as would my porcelain dishes.
Is there a weight limit on what we can bring? I keep thinking of more and more things…
Dropping a major battlefield commander like Alexander from a hilltop 500+ meters away might make even a handful of shots a game changer.
If you’re Kim Jong-un, your household item could be a nuke. Talk about impressing the yokels with weaponry.
I just thought how much more money my grandmother could have made if her household went back in time to the same era.
I mean, besides having six children to sell into servitude instead of just two.
She had the treadle powered sewing machine, of course, but also a handle crank powered washing machine with a hand-powered wringer. I’m sure that they had many more things which would be useful. They had a manual typewriter (look that one up kiddies!) which we inherited, and a real icebox, which was “powered” with blocks of ice.
My grandfather was a part-time cabinet maker, with plenty of high quality hand tools.
My great-grandparents raised their kids on a farm with no electricity, and most of the farm equipment was pulled by horses, so it would be more valuable for people in the middle ages.
I’m not sure if anything in my household would get me a fortune. My laptop with a full charge would probably be the best best, and hopefully get me enough money to get the hell out of Dodge before they realize that the battery doesn’t last forever.
I take that back. I’ve got my collection of automatic watches (no batteries) and my wife’s collection of costume jewelry with synthetic diamonds large enough to be impressive, but small enough to seem plausible.
M
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I gotta think a washing machine would top the list. Think of all the jubilant wives. The earth’s population would probably be much higher today if the washing machine existed back then. Happy wife = horny wife 
Per the OP, you get one (1) thing. That’s it.
If you’ve got a sword at home, that’s probably your best bet (no, you can’t have the bascinet, unless you want to leave the sword). Other than that, there’s your choice of a grab-bag of household items with no replacements and no way to manufacture more. Not worth much, if anything.
In my house, my most valuable single item would be a heavy 24K gold chain. Any other item on its own would be useless. I’ve got camping gear that would be an enormous personal benefit for going back in time, but any one item from that pile would be far less useful than a good knife.
If the rules were changed, I could put together a pretty decent personal kit for initial survival, but I have a fairly good knowledge of the ancient and medieval world, and because of that I know there’s not a whole lot in the way of portable personal property we have that they’d want.
Like I said before, most of our cool shit only works in conjunction with other cool shit. I call my iPhone "my external brain.” I use it for everything. Nearly useless without an internet connection, and dead in a day or so without a recharge. Weapons, great, until the ammo runs out; and the ammo is irreplaceable for decades, at least. And that’s if you’re a good field chemist and machinist who can adapt your knowledge.
Normal people going back in time would be just as fucked as a person from the medieval period being transported to New York or Tokyo. Actually, more fucked, considering we have social services to help people with no possessions, knowledge of the local language and customs, and no means of support.
You guys are assuming you can go back and “uplift” everyone. It wouldn’t work that way. Unless you’re a Society member or ancient warfare geek (like me), you are far more ignorant about everyday life in that time than you can even comprehend.
I know quite a bit about survival and wilderness living, I’ve been doing martial arts for most of my life, I know how to use a sword and I’m familiar with common armor, I’m in pretty damn good shape, and I love the crap out of learning about ancient life so I’ve absorbed a ton of information on various different periods. Even I would only give myself about even chances of making it through the first six months … and that’s with a decent kit to start with.
Starting the industrial revolution 800 years early with some crochet hooks and some dye? Don’t think so.