Toilet Paper. Perhaps this comes from growing up using 1-ply scratchy stuff, but as soon as I was on my own I started experimenting with new brands and now stick with one brand.
Tampons. o.b. only.
Mayo - Hellmans, but a little lasts a while, because I so rarely use mayonnaise.
I really struggle with sodas. My preference is diet Coke/Caffeine free diet coke, but I have, in the past, purchased the store brand. They end up being drunk very slowly, but I manage.
TP, but my wife still sneaks in some cheap stuff. 
Remind me not to take a dump at your place. The TP of which you speak comes with a metal serrated edge so you can tear it, just like a roll of wax paper. It’s Kleenex Double Roll dearie or it’s nothing at all.
Also…
Sheets, bed linens, comforters and pillows. Sheets and bed linens must be at least 300 thread count. Comforters and pillows must be down. I like to be comfy in bed.
At the same time I buy the cheapest toilet paper on the shelves. Go figure.
[ul]
[li]Diet Coke. None of that generic crap, especially no Pepsi (ugh!), no sugar. Just Diet Coke.[/li][li]Tissues. We’re not as picky about the TP as others here are, but the runny noses get ripped up by the rough stuff. Either Kleenex brand or Puff’s.[/li][li]Pop Tarts. (This one is my son’s.) The generic brands just don’t get icing all the way to the edges![/li][li]Peanut Butter - has to be Peter Pan. My son will only begrudgingly eat other brands, my wife won’t eat or cook with any other brand, I won’t eat any brand. ;)[/li][/ul]
On the other hand, sometimes it’s the non-good stuff. For example, bacon bits on salads and baked potatos? The family likes what they affectionately term “plastic bits”, the cheap stuff - no real bacon pieces for us.
Scott Tissue ONLY. Biodegradeable and NOT TOO THICK. I HATE really thick toilet paper. It makes my teeth hurt.
Panama Red.
Accept no substitutes.
Duke’s mayonnaise means security and home. I always have two quarts in the fridge and one in the pantry.
There is no more essential shopping trip than a Duke’s mayonnaise run.
Less essential comforts are Silk Reflections hosiery,Vanity Fair lingerie, Whole Fruit sorbet,Tanquery gin,and Lorna Doone shortbread cookies.
Diet Coke, no other diet colas, especially store brands. French’s yellow mustard…ONLY!
Salad dressing. I can’t stand cheap salad dressing, it always tastes like it’s gone bad. Oh, and I’ll second Colgate Total.
My Girlfriend and audio/video equipment.
Your teeth? :eek:
Try the other end. 
Crest toothpaste
Scott toilet tissue
Good shoes
Premium ice cream
I can live with most generics or store brands.
Don’t worry, lieu, after reading your many G.I. threads, I have no intention of letting you near my bathroom.
Wow, the first thing that came to mind when I saw the thread was toilet paper and paper towels, but I have to admit, I’ve agreed with a bunch of others here:[ul]
[li]running shoes[/li][li]perfume[/li][li]dress shirts (ew, those cheap see through kind are sooo nasty)[/li][/ul]
Although I haven’t seen anyone mention jeans here. I will not wear jeans if they aren’t Levi’s 501s. Don’t try to put me in a pair of $145 Big Stars - I just want my $40 Levi’s.
**Electronics and computer components. ** Ever try to get someone’s computer working when it’s made with all no-name cheap components?
Gas for my car. Acura RSX Type-S - MUST be 91+ octane, usually Sunoco.
**Performance parts for my car. **They HAVE to be as good as I can afford. I like to go fast, but I don’t want some cheap part getting me killed.
Car Polish. Zaino or nothing, thanks.
hmm… I’m sure there’s something very important to me that I’m forgetting… but in general, I can accept a less expensive alternative to almost anything not listed above.
[slight hijack]
Auntie Em, have you ever smelled your Viva paper towels?
They smell just like rotting meat. :eek:
[/slight hijack]
The list here may sound a bit odd…but here goes
Beer type drinks…SO… Newcastle Brown Ale … me OB (Korean and yummy)
Liquor… the hard stuff… SO… Goldshalager… me Southern Comfort
Soda…Pepsi all the way…spent way to much time working in a theatre that carried it…now it’s the only one that tastes right
Mayo … Best Foods Real…
Must always splurge on birthday dinners out…for Tristan and his brother…who share Dec 16th…it was Outback steak house for 7…
my personal favorite The House of Prime Rib in San Francisco
The SO will spluge on vintage reel to reel tapes…can you say HELLO EBAY???
Will add more after I get some sleep and the brain is working better.
Ms Xanax, I know what you mean about jeans. I only wear Victoria’s Secret sexy cut. They are the only ones that actually fit me. I feel as though I should stockpile because with my clothing luck, they’ll discontinue them and I’ll be up the proverbial creek.
Adams Peanut Butter is the only possible peanut butter. Both creamy and chunky reside in our house.
Q-tip brand swabs.
Montana Cricket has a thing for single malt scotch - but only good quality (read expensive). We also prefer quality wine and beer.