I've driven the kids across the country (FL to OR) 5 times now!
We usually stay in timeshares along the way because of the numerous food allergies & such. So I usually had the advantage of being able to shop and cook. But here are some tips, and I might come back to add some in.
-Nick's Sticks - organic grassfed beef sticks that are shelf stable. I buy direct from Nickssticks.com, and I buy the "wholesale" 100 packs at a time. You might see who likes them by purchasing them at Vitacost first before you buy that many.
-Costco has some strangely tasty crunchy broccoli product. It may not be at all Costco stores, as it's new to me. Ingredients are broccoli and palm oil, I believe.
Avocados (of course you have to time it right to eat them, but I find they are good travel food!), canned sardines, canned olives. Actually, just run down the canned food aisle at Costco and check it out!
Plenty of fresh fruits are fine without refrigeration.
Dried fruits and nuts
Trader Joes - has interesting shelf stable items
Oh - I would suggest that you invest in a cooler that plugs in in the car. The nice thing about that is that you don't waste space inside the cooler with ice packs. And the nicest thing is that when you take it into the hotel at night, you don't have to unpack it. You just plug it in in your hotel room. And if your hotel room doesn't have a mini fridge - no problem! (You'll need an adaptor plug though.)