Where are you riding? Does cross country mean coast to coast?
Most routes in the US will allow you to buy food at least every few days if not more frequently, so there is no real need for carrying much food unless you will be somewhere unusually remote. I'd say carry regular food and buy frequently, daily if possible.
Things that work well if you do need to carry them are stuff like foil packed tuna or salmon, boxed rice or potato dishes, soup or chili mixes. Things like hard cheeses and hard salami or pepperoni work well too. They may get greasy and nasty looking but remain tasty. Crackers, tortillas, chips, bagels, and other bread type foods keep well. Peanut butter, honey, and jelly all travel well.
Fresh veggies when you can get them and canned or freeze dried when you can't.
Of course power bars and cliff bars travel well as do gels and other energy snacks, but they tend to get tiresome pretty quickly. I like fig newtons, jerky, gorp, or baked goods for snacks.
In any case I'd stick mostly with real food and skip the protein shake mixes.