Do minor exercises to keep up circulation. Clap hands and move arms and legs occasionally. If more than one person is in the car, take turns sleeping. For warmth, huddle together. Use newspapers, maps and even the removable car mats for added insulation.
Cold weather puts an added strain on the heart.
Unaccustomed exercise such a shoveling snow or pushing a car can bring on a heat attack or make other medical conditions worse. Be aware of symptoms of dehydration.