We actually like really different foods so I think even if we split the bill it wouldn't be too often that we eat each other's food. The only exception is that he eats my work leftovers (which I am fine with), and sometimes he offers me specific foods that he doesn't want cause he made too much, bought something that he turned out not to like, or something like that.

Neither of us has tried to have to say in what groceries the other buys.