How to Make a Survival Stove (Car Heater)
http://tacticalintelligence.net/blog/how-to-make-a-survival-stove-car-heater.htm
Take an empty coffee can and pack it with a lighter, candle, and whatever.
The coffee can and a candle will keep you warm inside a car.
Keep it in the cab. Not in the trunk. If you get rear ended, your trunk may not open.