Have the ability to melt snow or ice, that is mostly what my tea candles are for, and a couple of nested containers, you can use your backpacking cup or cookware or a couple of washed out food cans with holes cut into one, or whatever, just put together something at the house that doesn’t take much space in the car, for instance a tuna can with holes cut or drilled allowing air for the tea candle, and a can that will rest nicely on top of that, it would be slow, but good enough for a couple of days running 24 hours a day.