I was in the Air Force in North Dakota for four years, and we all carried winter survival kits. A few candles to warm the car (with windows cracked), blankets, and food. But back then, it was either C-rations or K-rations, I can't remember which. Freezing had no effect, and all was in metal cans we could heat over a candle. (Be sure you have something to light the candle.)

I used to eat the meals in the spring or summer, so they didn't go to waste, and having been in the car all winter in below-zero temps had no effect on those rations. Of course, who could tell if there _were_ a bad effect on that stuff?

In North Dakota, water was not considered an issue in winter survival. If you got stranded, you had all the water you could want in huge piles outside your car. The issue was staying warm inside the car; blankets, thermal undies, and big boots. Everybody was told to carry a couple of candles and crack the window a little so you didn't die from carbon monoxide, and _don't_ keep the car running, as you could never be sure the exhaust pipe wouldn't be buried in drifting snow.

Mileages vary, locations and dangers vary, neeeds vary. Use your judgment and make your choices.