Well, a great deal depends on WHERE in the U.S. you'll be traveling. Food is very regional here. But a few things to check out might be:
Barbeque (also called BBQ). There are two very distinct schools - Eastern and Western. Western is also called "Kansas City" barbeque, and features a thick, tomato-based sauce. Eastern is thin with a vinegar-based sauce. Usually, what you'll find in barbeque places are pork or beef ribs that have been smoked using a variety of woods until cooked (the meat often remains pink, but is fully cooked) and the sauce is either brushed on the outside before serving or baked onto it. Often, there will be a side of sauce to dip individual ribs into before eating. Caution: Don't wear clothing that can be ruined easily! The sauce stains.
Mexican or Tex-Mex. This can be found anywhere, and features beef, chicken and seafood that is cooked with strong peppers, tomatoes and onions in a salsa. There are tacos, burritos, enchiladas, tamales, along with a variety of other menu selections. If you find a good Mexican restaurant, a couple of terrific desserts to seek out are sopapillas (fried puffy bread served with honey), flan (a cooked custard that's similar to creme' caramel), and baked ice cream (a scoop of ice cream that's breaded with crumbs and quickly deep fried so the outer crumbs toast but the ice cream remains solid.
Fresh water fish. These can include trout, walleye, bass, catfish along with some others. The meat is very delicate and flavorful, and are cooked in a variety of methods.
Those are just a few to start. I'm sure other people will suggest more things! Enjoy your visit!