i will give you my own thoughts about that scenario.

1. A head-on poses a risk of very serious injuries. And since one driver is already dead, the other can possibly be critical. One of the biggest risks is the arrival of overly-enthusiastic third parties who try to move the victim who is still alive ... because of the problem of possible neck/spine damage. It is not uncommon to see well-meaning responders do some very risky things (for the victim) while trying to "help". I am not against immediate critical first-aid. But definitely make sure you have immobilization devices like C-collar and a spine board would be excellent (but highly impractical for the average person to have a spine board).

2. Otherwise, how about good old-fashioned oxygen? It's one of the few things an EMT can administer that has a definite shot at really saving life! People never talk about oxygen, but getting someone on O2 might be a lifesaver while the ambulance is coming.

3. Be prepared for the victim to vomit. You will need to clean the mouth, maintain the airway, and ensure they are breathing.

4. Yes, some bandages for serious bleeding.

5. Small flashlight to check eyes and ears for brain damage & head injuries.

cheers, Pete2