Three Points of the Compass looks at a hack that might enable an upright gas stove to continue working in cold conditions. The Moulder Strip is only for 'extreme cold use' though and requires great care and is not recommended.
This type of re-usable heat pad has been around for a good few years now. The science is based around an old chemistry laboratory experiment with salt and water that was assured to wake up even the most bored of students.
Three Points of the Compass 