If energy were a little more expensive you could have jerry can sized packs of sodium acetate or similar. But noone really wants to fill up their boot with jerr

If energy were a little more expensive you could have jerry can sized packs of sodium acetate or similar. But noone really wants to fill up their boot with jerry cans and burn $3 worth of fuel for $2 worth of low grade heat. I wonder if there is a better PCM or thermochemical battery that could be worth moving on a not-train somewhere? Something that beats ice but works at not-4-degrees. Lye is okay but still a bit shy.