Foods can be uncountable, in the sense of different types or genres. For example, if you were talking to a child who isn't eating, you would say "Eat your food" or "Eat all your food", i.e. everything that has been served to him/her. But it is also pluralized when you're talking about varieties, for example: "Here in New York, we have food trucks that sell everything from hotdogs to falafels to vegetarian to tacos...all sorts of foods."

To add: it's books and food if you're talking about what you're going to do at the bookstore. Is this what you mean? Something like that? Or maybe you're just asking in general? You may be interested to know that 'foodstuffs' is a word, too. It has a different meaning and usage though.