They make these medium sized soft sided rolling coolers now--the inside is lined in a heavy weight plastic, with pockets on the outside for storing things.
Our best bet is to go to the grocery store and get:
veggies (as mentioned above) carrots, celery, radishes, cucumbers
lettuce for salads and sandwiches
1/4 lb of two kinds of meat for sandwiches
1/4 lb of two kinds of cheese for sandwiches
excellent whole grain bread
3-6 fruits, apples, grapes, oranges, peaches
A veggie dip for veggies and as a sandwich spread
jar of pickles
cottage cheese for salads
your favorite salad dressing
small bag of ice
a gallon of water
Milk if you drink it
At home or at a stop, wash and prepare all the veggies, fruits, lettuce, slice the bread, make the veggie dip, and make a sandwich to eat. Package everything in good grade plastic so the ice water doesn't saturate it.
Also buy: In the dry goods box, you'll need a knife, spoon, fork, napkins/paper towels, zip lock bags, cup, bowl, plate (disposables), S&P, tea, small cutting board, oatmeal, sugar, cinnamon (for oatmeal), graham crackers, pretzels, dried fruits and nuts (with or without M&M's), jar of Nutella, 12 pack of oatmeal snack bars, 6 chocolate bars, 12 marshmallows (if you like smores), bottled water.
If you buy these things at a grocery store, it will be less expensive and more nutritious than at a truck stop, though, I do understand you'll have to be stopping at truck stops anyways. You could probably get by with only having to shop at a grocery store and do preparation once a week.
We've done this in preparation for a driving vacation from home, and we've done this in cities we've flown into and then traveled by car.
I've heard but haven't tried heating up food over a part of the engine, the food wrapped in heavy duty foil and after 50 miles, it's hot. That might be a way to add some hot food to your menu. Good luck, let us know how you did.