Carbohydrates come in two main types, simple and complex. Simple carbohydrates are sugars. Examples are breads, cereals, beans, pasta, etc. Trail mix is a good snack food for the day-long lunch. You can also mix your own and put in exactly what your Scout likes.
Most trail mixes consist of dried fruit, nuts, seeds, etc.
You can also throw in a little shredded coconut and some dried banana chips, if he'll eat them. Other good things include shelled sunflower seeds, carob, mixed nuts, pretzel sticks, or the little Japanese cracker-like snacks. By comparison, one pound of trail mix will last for a week in the high Sierras. Whatever you get for him, make sure your Scout likes it by having him try it at home first. Bagels, or the small bagelettes, are great breads to take along for the more substantial food break around noon.