Road flares, the red ones sometimes called "fusee's" are good to have. they have their own igniter, can be had in different burn times and have many uses. Along with some emergency reflectors (the red triangular kind truckers use) they can help keep you from getting hit by a plow or traffic if you go into the ditch in snow. You can start just about anything on fire with a road flare, including a spare tire for daytime smoke signalling.
Where I'm at, freezing temps are the norm. There are small emergency water pouches, in mylar that are Coast Guard approved and are partially filled so they won't explode when frozen. You have to have something to thaw frozen water out (or snow) for drinking. If you use a tin can burner or any open flame in a stranded vehicle, you must leave a window cracked open to get fresh air or you will die from carbon monoxide poisoning. If you get even a whiff of gasoline, don't light anything and immediately check for a fuel leak. This also goes for using the vehicle heater (if the engine still works). The tailpipe must be clear of obstructions and a window must be opened for ventilation. Run the engine only for short periods to save fuel. Someone should remain awake while the engine is running.
I keep a -50 degree sleeping bad system in my truck. If I have to overnight in the ditch, at least I'll be warm. A shovel and some coffee cans of sand and salt are also a good idea, along with a pair of "pak" type boots and spare wool socks. I use lithium batteries in my flashlights because they will work much longer in the cold than alkalines. I'd add a jar of peanut butter and a spoon to your munchies. It is calorie dense and will give your "inner fireplace" something to burn.
On the physiological side, don't drink alcohol or smoke; they both will lower your body temp. As weird as this sounds, if you have to pee, do it (outside of course). Holding in urine uses body heat. Put on a good hat or hood. You lose lots of body heat from an uncovered head.
This is getting a little long, but one last thing. Unless you've gone off a remote mountain logging road and nobody knows you're there (with no hope of rescue), stay with your vehicle, maybe even then. It can provide you with much of what you need to survive. Make your vehicle as visible as possible, perhaps with a large piece of blaze orange plastic on an antenna or a stick, or your flares and reflectors.
