A lot of "luxury foods" would become rare. Yes, the U.S. could certainly feed itself, but the vast selection of produce, meat, coffee, etc., that Americans are used to seeing in every supermarket and convenience store would disappear.
As for food, we're fine. We export quite a lot of grain and such; the only stuff we import is fruits and such that can't be grown in the US. If pressed, we could grow enough of everything to keep everyone happy. However, one note: we can't grow coco beans in the US ('cept in Hawaii, I guess), so chocolate would be quite rare. Might be a good side note in your story.