All hail ice packs.
I have a bottom freezer half full of them, left over from my injured knee recovery. Damn, those things are handy.
For injuries that don't involve actual spillage of blood, the first thing that first aid seems to recommend is 1. Stabilize, 2. Ice Packs.
Since I'm not in the medical profession I'll bypass 'stabilize' and move on to Ice Packs.
What I learned during my knee injury is that I'm supposed to ice my injured part no longer than 10-20 minutes. Take the ice pack off and wait a while (half hour to an hour) then repeat. Usually, I only use the pack for 10 minutes and don't have to repeat it. However, in the middle of a back spasm (too much overhead weight lifting) I'm using them for 20 minutes.
After 36-48 hours I've read to alternate the ice pack with heat. I prefer a hot shower, but heating pads or a hot water bottle work just as well.
1. I found the bendable ones from the drugstore made of cubical cells filled with blue liquid to leak. I don't recommend those. These are sometimes called 'ice blankets'. Note, some brands contain propylene glycol and can raise a rash if they leak. If you go to the hunting section of Walmart or Target and find bendable ones with little square cells, check to make sure they contain water. Even if those don't leak they won't raise a rash or stain your clothes. The ones from the hunting section haven't leaked so far. They appear to be sturdier than the ones from the drugstore.
2. In the drugstore, the ones that I like are filled with a mixture of clay that makes them bendable even when frozen, and are pretty sturdy. Other than clay I don't know what's in them, but I've never had one leak. The ones I bought have a fabric bag to hold the ice pack, and a stretch belt. These can be worn while you're walking around.
3. I found some heavy duty square ice packs made for food storage. The small ones are okay to stick behind my back while I'm driving.
4. The ones that have little 'peas' inside them. Bought one. Used it once. Threw it away. Held the cold about 15 minutes.
So there's my little survival tips for injuries for when you need an ice pack.