You're actually better off buying beverages such as juice and milk from the store brands. That's because they're produced regionally and are less processed than their brand-name counterparts. Also since transportation is less of a factor, quality is fresher.
According to Consumer Reports, a panel of trained tasters reported that a Publix store brand juice ($2.99/carton) tasted better than the Tropicana ($3.48/carton) right next to it. There was also a 60% cost difference between store-brand milk and brand-name milk.
However, soda is a different story, as many people have strong opinions. Some recommend buying soda generically, although generic versions of soft drinks can vary widely in taste. The ingredients are mostly the same -- tiny variations in flavor can create quite different versions of the same drink. If your taste buds aren't picky, the price of generic soft drinks can't be beat.
(Image via Flickr)