Just recently I bought a flameless cook box. It works with a chemical heater like the ones in MRE;s. Just add water to a pouch of chemicals and it starts to heat up.
Now I don´t have car but reading this it hit me that it would be a practical thing for car survival kit. Works without a flame and only gives away non-toxic fumes and steam so it is harmless to use inside a car.
Certainly a good morale boost to get a hot meal if you´re stuck in the snow and it keeps you warm.

A video explaining how it works: http://youtu.be/Xp90ZNVlY1Y