Just to add one thing that nobody has mentioned yet - if the route you take entails quite rugged terrain or sustained grades, you might want to consider a pair of collapsible trekking poles. While over a long hike, use of poles requires a bit more energy and will tire you faster, it can serve to significantly reduce stress on your knees - which may be the more important consideration on a multiple day excursion.
My guess was military.
How much time do you have to train, and how much money are you willing to spend to do so? There’s a machine called an incline trainer that really helps prepare you for hiking up hill. It’s essentially a short treadmill with a very steep incline (mine goes to 25%, I’ve seen them as high as 50%). Unfortunately, they’re expensive ($800-2200, depending on brand).
Other than that, getting out and walking with your gear on is the best way to get a feel for your speed and level of fitness. 4 MPH for me is a flat-out run, but I have short legs. I wouldn’t be able to do 15 miles in a day unless the terrain was level or mostly down hill.
Since you plan to stay in a town at night, you can get by on less food and fewer provisions, but you do need to account for any unseen possibilities, such as not making it to your destination on time. You might want to make sure to have a poncho and a traveler’s blanket with you, in addition to some food, water, clean socks, and a change of underwear. Other than that? Maybe some bandages or other basic first aid.
Just an aside: these days, it’s damn near impossible to fly anywhere with any kind of stove in your luggage, checked or carry-on, so if you wanted to carry one, you’d have to buy it at your destination.
Yes, yes, and again yes! I recall seeing an estimate somewhere that using poles on both uphill climbs and downhill runs reduces the pounding on your knees and ankles by something like 30%. They’re also great when you need to cross a small stream, especially one with slippery rocks and/or swift water. Make sure they’ll fit in your checked suitcase/backpack, since some security folks won’t let you carry them on (though others will - it’s not consistent).
Goretex rain jacket (with hood) and pants, good. Poncho, bad. If there’s no breeze, you just sweat under a poncho - if there is a stiff breeze, a poncho blows around and doesn’t keep the rain out.
I did a bit of hiking/hitch-hiking in Europe when I was 18. It was late summer, early fall 1980. Most of the hiking I did was in Wales and Scotland. I started off with an external frame pack, and after a couple of weeks hauling that thing around, and trying to make it fit into people’s cars, I bought a smaller internal frame pack and sent the big pack, plus some clothing and books home. If I really needed something I bought it along the way.
I did the town to town thing mostly on roads, but did hike up some peaks (Ben Nevis, Snowdon, the Pap of Glencoe) but only after leaving my pack behind. I wore those big circa 1980 Vasque leather hiking boots with vibram soles. I don’t remember what socks I wore. All I can say is make sure your boots/feet are good and broken in when you start. It’s no fun if your feet hurt.
Food-wise I ate mostly in pubs, fish and chip stands, and occasionally a restaurant. After a month of UK ‘cuisine’ I sought out the Chinese restaurant in whatever town I happened to be in. I always had sandwich supplies just in case but otherwise didn’t carry a lot of food. I don’t remember carrying much more than a canteen or two’s worth of water at any given time.
I often slept in youth hostels and bed and breakfasts but carried a tube tent in case neither was available, which happened a few times. A rain suit - hooded jacket and pants - is essential.
I had my money supply and passport in a moneybelt that I had secured around me under my clothing at all times.
Lots of good advice here. A lot of it is contradictory, but hey, YMMV. Literally.
Some random thoughts:
A good book to read is The Complete Walker by Colin Fletcher. It’s pretty outdated at this point, but it is the best book I know of to help you get the sense of what is involved in multi-day trips. It’s really thick, but fun to read. I’ll second Julius Henry suggestion of checking out Ray Jardine’s book. Please keep in mind that Ray is completely nuts in his pursuit of ultralight pack weights, and I think most people would be pretty miserable doing things “the Ray way.” But he has lots of good thoughts and insights about how to trim your pack weight. Plus, it’s a good read.
A training tip–Go grocery shopping! Choose a grocery store that is several miles away. Do some grocery shopping, load the groceries into your pack, and walk home. This doesn’t exactly replicate what you’ll be doing in Europe, but it’s a way to get some miles in without feeling like you’re taking pointless walks.
Socks–I used to use thick wool socks and sock liners. Then I discovered Smartwools. Now I just wear the one pair of Smartwools, and never get blisters. They’re expensive, but a great value.
First-aid Kit–bring plenty of Moleskin! Also, remember that a lot of things that are cheap and easily available here in the US are darn near impossible to find or wildly expensive in Europe. I believe some ordinary OTC drugs fall into this category. See a recent travel guide for more info. If you take prescription drugs, make yourself 2 sets, and store in 2 separate places, in case one gets lost or ruined.
Shoes–Make sure to bring a set of lightweight comfortable shoes. You’ll want to take off your boots at the end of the day.
Also–pack a couple of emergency powerbars. I doubt you’ll have any problem finding enough to eat as you go (depending on where you are, of course), but you should have some emergency rations.
Ultimately, the lighter your pack is, the happier you’ll be.
The boots are a key thing in your pleasure. Try on lots of pairs. a good outfitter should know how to make the boot also fit your foot better by breaking in the toe box, etc. Also a good insole so that your arches do not get sore. I would say Gore-tex is a must but I am sure some would disagree.
Read reviews on a water filters and know where the water sources are.
Take more food than you think you’ll need. Backpacking burns lots of calories. A few nutrition bars can go a long way.
Make sure your tent is waterproof and carry seam seal. A wet sleeping bag is a miserable thing to sleep in.
I also have to agree with the ziplock bags. They are great for keeping your maps ,clothes, etc dry and work great as garbage bags.
15 miles a day all depends on what you do now. I know people that won’t do more than five miles a day and others that can breeze through twenty. You want to enjoy yourself as well.
Hope you have a great trip
Oh, and make sure any foods you get are easy on your stomach. Especially stay away from anything (including nutrition bars) with sugar alcohols in them. Many, if not most people find that sugar alcohol causes stomach upset, including diarrhea. That’s the last thing you want when you’re in the middle of nowhere.
Be sure to pack lots of bandages. Aside from the obvious emergency uses, they’re also really handy if anything starts chafing.
duct tape is a must. small roll picked up at the local hardware shop can be used for all kinds of things. repairs, blisters, rips, etc