I don't really know much about the import/export bit, but I think the U.S could likely get through with all their own food. We've got steel plants and such; in fact, there's a large one in Buffalo. There's plenty of oranges in Florida, apples in New York, and grain and wheat I think are grown in the plains area. there's some corn in rural areas too.
Do you think the States would be able to produce enough on its own to get by decently in twenty years? How much of your total food do you import, do you think? Because with the energy crisis, there's won't be as many imports/exports.