Here’s an amazingly clear-headed and complete list of things you should put in your car in case of an emergency. Snip:
For heating water inside your vehicle or on a car hood, you will need a metal container of “canned†heat, typically sold at grocery stores to keep food serving trays hot. If you have the space, keep several handy, but one should last several days and is reusable, thanks to an air-tight cap.