Stay in the vehicle. Do not leave the vehicle to search assistance, unless help is within sight. You may become disoriented in the blowing and drifting snow.
Display a trouble sign, such as a bright cloth hung on your antenna. If you have flares, set one up on the same side of the road, about 50 feet toward the direction of oncoming traffic and another at 100 feet.
Turn on your flashers (4-ways or hazards).
Turn on the vehicle for 10 minutes every hour & run the heater. While the engine is running, turn on the dome light. Be sure to keep the exhaust pipe clear of snow, and roll down a downwind (look at the direction the snow is blowing) window slightly for ventilation.
Watch for signs of hypothermia or frostbite. You may need to run the heater a little more often, but be careful of the fuel usage. Contact the American Red Cross to learn more about the trouble signs for hypothermia and frostbite.
Do minor exercises to keep up your circulation (clap your hands, move your arms and legs occasionally). Try not to stay in one position very long. If there are passengers, huddle together and take turns sleeping. Use anything you can find for insulation (blankets, newspapers, even your car mats). If you cover two people up with one blanket, you will get more warmth.
If you have a candle, you can light it. It will produce some heat and light, if at night.
Conserve it, but make sure you drink some water from time-to-time. Same goes for high-energy bars. Do not drink caffiene or alcohol based drinks. They both hamper your bodies ability to cope with the cold.