First aid could easily be a couple of threads in itself.
Unfortunately it's more involved than making a list of supplies. Anyone can find such a list on the internet. Under
"first aid list" on Google you have 47,400,000 listings. Of which 47,000,000 are probably simple repetitions.
For those that just want to
buy a "first aid kit" all I can say is good luck, and don't buy the cheapest. And hope that you, or someone that you care about, will find a person that knows what to do with it.
The problem is that we all think that we are very knowledgeable, in a general sort of way, about everything. I'm not trying to put anyone down. But the fact is that "a general idea" about first aid is not enough.
For a background - I was an EMT working in an 800 bed hospital's emergency room as an Orthopedic Technician. In addition I taught American Heart CPR at the hospital, and Red Cross CPR outside the hospital.
To better learn first aid I taught a course that is no longer listed, Advanced First Aid and Emergency Care, for the American Red Cross. Sadly, I see nothing like it on the Red Cross or Boy Scout sites. There are classes that you can pay for, but I have no way of assessing them.
If anyone is interested, the second edition of the book I used in class is available on Amazon (the 1981 issue) -
Advanced First Aid and Emergency Care.
As a serious joke I used to tell people that there were 3 kinds of first aid. In Red Cross first aid you placed a sterile compress on the wound. In Boy Scout first aid you placed a clean handkerchief on the wound. In military first aid you pressed your dirty hand on the wound to stop the person from bleeding to death.
Speaking of a "sterile compress", sanitary pads are very good too. No joke.