how much danger to put oneself in to rescue others etc. - my training didn't cover any of that and I'd just have to deal with it as best I could, as any non- specialist would.
You shouldn't be putting yourself in danger to rescue others. That's always been clear to me in first aid training, and particularly with water based. My most recent qualification is first aider at work (where it's also clear you shouldn't put yourself in danger) - the first thing you should do is check for danger. Better one dead casualty than a dead casualty and a dead rescuer.
But my first qualifications were lifesaving, so water based - I haven't done an RLSS qualification for 30 years, but while some aspects of resuscitation have changed, I would imagine they're still much the same for the order of least risky rescues, which I think were reach, throw, wade, row, swim. Basically, you avoid getting in the water if you can, because that increases the risk. Hypothermia/cold, underwater objects, fast currents.)
But even out of water, you need to think about road safety, risk of falls, chemicals, live electricity, risk of falling objects - all depends a bit on the environment.
My first aid courses have always dealt with how to deal with bystanders- ask them to move back, give space - but give them jobs, too. Get them to call the ambulance (and come back,) get them to help with casualties - they can put pressure on a bleeding wound, get coats for warmth, even help with CPR. It's always been covered in the courses I've done (RLSS, Red Cross, St John Ambulance.)
In reality, I've never had to deal with anything major, and knowing the theory might not mean anything in practice.