It's my understanding is that, by the letter of the law all "international" trash, which includes any food that could spoil, must be discarded before entering the US. Our briefer hinted that if we only had aboard food/drink that was unopened, sealed and not going to easily spoil (think a box pop tarts in the unopened original packaging vs. a new unopened loaf of bread) we would be okay. This was our second trip in three years and never any hint that we might be inspected. In fact, this time they didn't even ask.