Can't stop off at a WalMart that has a grocery? They are usually near freeways, HUGE parking lots where you can park a semi or large truck for a few minutes - just park it a bit away and get some walking in to boot. Check out the deli counter and surrounding area where you could get meats, chicken salad, or Soups. There is also lots of small containers of yogurt, cottage cheese, cheese sticks...
Any IHOP, Cracker Barrel, or Denny's restaurant can do up some scrambled eggs with cheese (and later sausage/bacon). I ate that for Breakfast and lunch. And most of those places serve soups too.
And definitely pack a cooler or fridge installed if you'd like to save money or time. Love the idea of getting a small one that runs off of the truck's electrical.