I won't even dignify them by saying that they are "better than nothing", because they aren't. All they do is give people a false sense of security. Most people will do better to remember to dial 9-1-1 in a hurry than to have one of these around.
You also have these. Most people think of them as a "military first aid bag". They are, sort of, but aren't, really. They are larger and actually contain more and more useful stuff. You actually need some training, most of it fairly basic, to make effective use of one of these. They are a handy thing to have if you're an EMT, perhaps. Of course, an EMT would probably build their own. A group of people that are prepping together might have one to go along with a more in-depth stock of medical supplies and a couple of people who are trained to use them.
Then we have something like this. There are a number of versions of them out there. This particular one is the well thought of D.A.R.K Trauma Kit from DARK Angel Medical. It can be customized to some extent depending on your needs, and contains the gear you need to help someone who has suffered a serious traumatic injury, such as a gunshot wound or an explosive amputation. It is specifically not for bumps and bruises, folks. You should have a well-stocked medicine cabinet for that sort of thing.
Being a cheap bastard, I didn't spring for the DARK Angel kit. I built my own. Actually, I built several. One travels in my range bag, because it's a range bag. Even though my range seriously stresses safety, it's one of the places I go to where a gunshot wound is most likely to happen. They have trauma bags spotted around, and I have my own.
I keep one in each vehicle. Vehicle wrecks are violent things, and body parts can be removed. As has been pointed out in other posts you'll find in this same label, a tourniquet is the gold standard to keep an amputation victim from bleeding to death before they can get to "real" help.
Writing this, I need to build one or more for my home. Home defense happens, and I have power tools. Amazing what you think of when you're explaining something to someone else.
What's in my kit? It varies, but in general (links go to Amazon, buy the stuff wherever you want):
- Paramedic sheers. Get the good titanium ones, they'll cut almost anything.
- Israeli trauma bandages. They come in 4" and 6" sizes. At least one of each size; more is better.
- An Adventure Medical Kits Tramua Pak. This has gloves, gauze pads and a QuikClot clotting sponge.
- QuikClot guaze. You might need more than the sponge.
- A C-A-T or SWAT-T tourniquet. Two isn't a bad idea, really.
- A bag, your choice of what kind, to store it all in.