Can he take a small cooler with an ice pack at least? I'm assuming he can. I've found many pasta dishes, especially those with red sauce, are still good when eaten cold (sometimes they're better that way!). That might be a good meal for him since the carbs will give him the physical energy he needs. You could puree veggies to put in the sauce, as cold veggies often aren't very good whole. Also, I've had this recipe saved for awhile for peanut butter and jelly "pockets": www.thekitchn.com/recipe-whole-wheat-doubl
Another option for sandwiches is to roast up chicken breasts or a pork tenderloin, then slice somewhat thinly and use that for your sandwich meat instead of lunch meat. It has a ton more protein and way less sodium, and will be a lot more filling for a sandwich than lunch meat is. Use sub rolls or buns to make them easier to eat than regular bread, since the thicker meat does tend to be heavier.
For snacks, stuff like nuts, beef jerky, and fruit like bananas, apples, and oranges, do not need to be refrigerated.