It feels early in the year to be talking about cold as a potential emergency, but I wanted to bring it up before it has time to hit hard. Seems crazy, being in Texas, but people are affected by cold weather here pretty badly. They own light jackets - if any, no scarves, no mittens, inadequate hats, laughable footwear, thin socks - if any, and no longjohns.

There are lots of hand-warmers available at grocery stores, at amazon, at sporting goods stores, and elsewhere. Many of them are shaped to go into mittens or will stick to the bottom of your sock.

The problem is, those are usually once-only options. To a liberal, they're "not green" because they usually end up in the trash. And then all that lovely iron inside goes to the landfill.

While most homes can handle putting a wet cloth into a freezer baggie (they're sturdier than regular baggies,) and microwaving as needed - perhaps wrapping in a dry cloth to prevent burns - it's not an option away from home for most.

One option I want to recommend is snap-disc style, reusable warmers. The liquid crystal heats when catalyzed by the action of snapping the slightly concave metal disc inside out, and back. I'm sure that snapping the disc causes the metal to warm slightly, or shed some atoms, or something. The liquid crystal heats up to 130F fast, and will stay hot for over an hour in a coat pocket. With several, used one at a time, you can keep the feeling in your fingers all day if you have to. Often sold in sets, with a few large & medium pieces, and some small ones. Since they have to be re-set in boiling water, the large ones are best set aside for emergencies.

Another option is a catalytic heater, just a pocket version of the ones you'd use when camping. The disadvantage that comes to mind first, is that any kid with a lighter, matches, or item that has been lit, is likely to be jailed on suspicion of wanting to burn down the school. A friend who plays guitar uses one that he fills with butane and lights, it seems to ride in a jacket pocket just fine so far without doing any damage. It also just occurred to me that even a very clean-burning catalytic heater may cause a coat to release aromas (of laundry soap, or whatever) if used while hunting.

For true emergencies, you can get a blanket or bivvy that is much like those thin, easily torn, cheap space blankets. The better blankets, and the bivvy style, are sturdier, do the same job, and can be pulled up around a sleeping bag for a moisture barrier/insulation layer. You're likely to sweat in one, which also has risks, but depending how cold someone is, or how at-risk they may be due to physical condition, it can be worthwhile to have.

The options are out there. If you have to go cheap, the disposable ones will do. If you can, and prefer "buy once, cry once" style shopping, there are options.