Posting in another thread reminded me of an item my buddy purchased in Las Vegas. Perfect to store in the car or wherever.

You know those hand warmers you get in sporting goods stores? Costly but nice to have in a deer stand. Well, these are larger hand warmers and get bigger for abdomen/back sized. (Which also work great on sore or aching joints) You click a button in the corner and it heats up the entire pad with the chemical reaction and stays hot for hours. I don't recall the time but it was 6 (I think more like 10 hours.)

Great for cold mornings or emergencies. They're reusable by boiling them.

I live in a warm area and have a bunch of extra hand warmers on hand. That being said I need to buy a couple to have on hand. Those with wife and/or kids, would have the relief that if something happened and you needed warmth, this should satiate them and relieve stress from them whining :D

http://www.clickithotpacks.com/

I have zero affiliation with them. Just thought this would be a good survival tool that you can use pretty regularly.

I got to try these exact same packs at some dumb horse show she dragged me to this weekend. No idea how long they last or how many cycles they will continue to give best performance, but the one they laid over my shoulders felt like pure heaven. I'm thinking about buying some for Xmas gifts if I get good feedback on what they are like to live with.

I know both the hand one and the large pack were burning hot after 4 hours when I left his house. I didn't put it on my back as it was his but I could imagine how good that would feel when I get aches.

He's used it a bunch. I'm sure after so many times it starts to degrade like any other product but it seemed to me worth it. Summer rolled in and I didn't need it then. Anyways, it seems gimmicky but like you said, once you try it you think "wow it does work." And boiling and cooling it does indeed restore it. Pretty neat.

Scuba divers used to use these in cold water back before every one went to dry suits.
They work well.