Thanks all. To restate, I am looking for a medical first aid kit, not survival kit, although I realise some stuff applies to both, gaffer tape and a knife being good examples. But I want a compact pure, hardcore, 1st-aid kit that will always be in my bag as opposed to bulkier stuff appropriate to each particular flight. I imagine this being used by well trained 1st aider or a medic of some kind.
I had not considered pain control -it’s a good point. (Sycamore up thread has pointed out a Canadian military film about post crash 1st aid. It has realistic simulated injuries, but completely missed the most stressful factor of everyone screaming or groaning or worse.) I’m not sure of the legality and shelf life of eg liquid morphine, I will do some local research on that.