I've gone through different versions of things, but right now in our Honda Odyssey (I have a wife and three kids):

--A jar of peanut butter
--a small loaf of some German rye bread that's vacuum-bagged
--a few cans of Italian wedding soup
--about 10 Clif bars
--tea bags and hot chocolate packets
--Some loose hard candies (Jolly Ranchers, Werthers, etc.)
--6 1-liter Nalgene bottles
--an old mess kit with utensils
--an Optimus 8R or a 2-burner Coleman propane suitcase stove.

After a 9+ hour stint locked on unmoving interstate traffic last year, the only thing we used was the water and the Clif bars. I also usually keep a Lock and Lock container in the front stocked with random trail mix/granola bars to keep the kids going if they grumble about being hungry between meals.