Speaking of Beef Stew....
During my deployment to New Orleans with the Red Cross, we were often given "heater meals" of beef stew. These consisted of a double walled can. Beef stew in the center and a combination of a water bag and (I think) baked limestone in the outer can. You punched a hole in the water bag and it caused a chemical reaction that caused the limestone to become hot. Heated the beef stew in about 3 minutes...realllllly hot!

I have not seen these on the market anywhere. Good stew too. Would be perfect for vehicle use. Actually that is where I ate most of them. Worked great.