The specific food restrictions change relatively frequently, and sometimes enforcement is a bit variable. I think most commonly restricted are fruits and veggies (particularly ones with seeds such as peppers and tomatoes) and meats, particularly if not commercially packaged by a store. I generally don't go out of my way to alter what I'm carrying, and just answer any questions at the border accurately and truthfully and if requested surrender any food that happens to be verboten at the moment. So far, that has worked out just fine.
It probably goes without saying, but take very careful care to obey firearm restrictions. The penalties for failing to do so are significant.
