A little-known cause of chills, headaches, and ill feeling in winter is dehydration. When the body runs low on water it conserves fluid by reducing circulation to the extremities, which means your hands and feet freeze quicker. Guzzle water before going out under the stars. Safety Cold can kill. If you observe from a remote, lonely site in winter, think through the entire chain of events that will happen if your car won't start.
Car batteries lose power in the cold.
Even if you normally run your equipment off the car battery and have enough juice left to start the engine, don't assume you can do this in unusually low temperatures. If in doubt, run the engine for five or 10 minutes per hour while observing. A candle in a car will provide much warmth if you huddle over it, but open the window a crack. If the engine will start but the car won't move, check the gas gauge. Conserve gasoline by running the engine and heater only 10 minutes or so out of each half hour or hour.