I'm pretty thrifty overall but have found a few things that need to be brand name.
Glad force flex trash bags is a biggie.
Dish soap. (I have moved up in names and am only at Dawn and that leaves rings on my counter, I don't know what the next step up is but I'm going to have to upgrade.)
Scented things. (I tend to like Yankee Candle brand stuff or febreeze)
and my newest is apple juice- apparently the store brand stuff is really yukky.
Laundry detergent- (only because I'm active, a nurse, and own a dog), like some serious odor removal, and Tide has some good products, but I was also thinking of trying Arm and Hammer. Expensive coffee is nice once in a while but I go through too much so I usually just buy one of those huge things of Folgers. I try for organic foods but am not intense about it.
On the flip side- cheap brand canned soups seem to be fine, generic store brand OTC medicines, lower priced yogurt and cereals, many more.
I buy a lot of stuff in bulk. My house may as well be a pharmacy and convenience store.
I'm super clearance and comfort oriented on clothes. We have a Savers nearby, and since the general population here is upper middle class, hand me downs end up being nice anyway.
Appliances and stuff- I do some research, mid price and known brands are usually safe.