How to keep food fresh when camping in summer?

Canned food is never a worry, but other food that I want to bring - oranges/bananas/bread/dry cereal - these things can be kept well for a while without a refrigerator, but surely they would go bad/yucky in heat (temp can sometimes rise here to 100 F, but that's a freak day, usually summer 80-90. Still, that's pretty hot, and I'd like to camp for several days. The car is even worse because heat builds up with the gl (and it's black). I had an idea to dig a hole and make an improvised 'storage pantry' - in the ground, in a shady area. Just dig like a foot or two down, wide enough for the food and keep it covered with a improvised wooden cover - would that work? Or does the earth absorb a lot of heat? Of course I could just check by burying a thermometer and checking it after a while. What do you guys and gals think of the idea? Or do you have a better solution? (using coolers and ice bags isn't really an option either, it would only last for a bit, and I want to make a rather long trip)