For most staple beverages like orange juice and milk, you're actually better off with store brands. Because they're produced regionally, there's usually less processing and transportation involved than with national brands, which impacts quality. In fact, a panel of trained tasters told Consumer Reports that a Publix store brand juice ($2.99/carton) tasted better than the Tropicana ($3.48) next to it on the shelf [source: Consumer Reports]
On the other hand, generic versions of popular soft drinks can vary widely in taste and quality. While the ingredients are mostly the same, and the price can't be beat, this is one market that makes a lot of noise about tiny gradations in flavor, even between different versions of the same drink from the same manufacturer. It's worth trying store versions, which have been known to fool blind taste-testers, but most people have been attached to the same soft drink for most of their lives, and the subtleties often matter to them.