The main 2 necessities are beef jerky (preferably teriyaki flavored) and peanut M&Ms. That'll hold you pretty good, if you get stranded by heavy rain or something. Most grocery stores have pretty good deli sections, if you can't find restaurants. And pizza is a good option, just fold 2 slices together, like a sandwich, and use large zip lock freezer bags.
And definitely fresh fruit, wether free from nature or paid for.