Anything that’s basically one ingredient or one active ingredient. If you’re buying ibuprofen, for instance, there’s zero reason to buy the name brand (Advil) vs the store brand.

Past that, there are some store brands that are actually a big brand. The big brands do that so they can get the bigger margin selling as a name brand, but more volume selling as generic. Costco is and example of that - many Kirkland products are made by major brands.