Cheerios: You would think it would be hard to mess up this kind of simple cereal, and a huge box of generic is so much cheaper than the original. But I realized right away that the generic has almost no staying power and turns soggy the moment it gets wet! My situation may be unique since I eat cereal with juice (strawberry kiwi, to be exact) instead of milk, but I'm switching back to real Cheerios to get the crunch back!
Metamucil: I'm not ashamed to say I like drinking a glass of fiber to keep my pipes running smoothly, so I had to try out the grocery store brand since the savings is giant on this one. However, while name-brand Metamucil mixes up nicely almost like Tang, thie grocery store brand is more like gross sawdust floating in the glass. I'm definitely going back to the expensive stuff!
Kleenex: I can go either way on this one, but the generic brand definitely has some quality control issues on the perforations between each tissue. If you aren't careful, you can easily pull a whole bunch out of the box at once, which is so annoying! It's kind of pain to rip them apart like paper towels.
Floss: At last, I think we have a generic winner! I like Glide floss, which is kind of top-shelf expensive, while the generic equivalent is a couple dollars less. So far I haven't noticed a difference, and the generic even has a little more mint flavor to it, which is nice. This is one of the biggest price differences I've tried, so it's nice that I actually like this product!