Knife and gun to kill a fat guy, slit him open, then crawl inside to wait for the Rebel Alliance.
There are drinks which freeze less readily than water, but it would still be very cold and lower her core temperature. (Plus flash freeze once opened.) Better to put hot water into a thermos before she leaves. Then she can add Hydralite, instant coffee, Koolaid, bouillon, etc. to have a hot drink and pick-me-up. Beyond that, small survival pouches of water stored under the driver's seat should thaw fairly quickly as she runs the car heater. You can also get self-heating survival rations. Very seldom is anyone trapped for longer than 24 hours, so it wouldn't be too expensive.
If you spring for the Jump-N-Carry or similar, most also have a 12V accessory port, which means she can carry a cup warmer, food warmer, or 12V travel electric blanket. I'd calculate how long it would run though, so worst case she gets stuck over night, she doesn't use all the battery before the coldest part of the night. And it's kind of either-or; if she runs a 60W travel blanket for twelve hours, it probably won't have enough left to boost the car.
One concern for me would be how she carries such heavy items so that they are accessible without leaving the car (and losing all that heat) while not having potential missiles in case of an accident.