Food storage should be rotated regularly to ensure maximum freshness. Leaving a food stash in a hostile environment (like the inside of car) means that it's not going to last very long, no matter what you do.

Food in my car never lasts long, anyway...because I eat it when I forget to eat before I leave home, and I'm on the road a lot. I just have to try to remember to replenish it frequently, which is a good thing, as it keeps the topic fresh in my mind.