The only food that I know of that will last in a car's trunk in a high temperature environment are "lifeboat rations," which are supposed to remain good for, typically, five years. But if you are just storing a few days worth of food, you could also get pretty much whatever you want and replace those items every couple of months.

I have lifeboat rations in my trunk bag, along with some Gatorade, tea and small snacks that get rotated regularly. I also use the quart+ sized water jugs from the grocery store, rotated regularly.