I don't driftboat, but raft whitewater. Understanding you're asking about what you need for drifting:
Lots of rafters I know carry something like the NRS Pro Paddler
first aid kit as a starting point for day trips, overnights and for each boat to have on multi-day trips. It's got lots of things you'd want and can be supplemented with extra tape, trauma bandage(s), extra meds, CPR mask, etc. when desired. Folks going on more significant trips will want a much more comprehensive kit with the group.
For training I personally think everyone should have at least Basic First Aid & CPR as a start, then move up to Advanced.
They say most boating accidents happen within 10 feet of shore, so I'd expect your risk rises when you pull over to shore, tie up, and go wading. And you never know when you'll be the one rescuing yahoos that didn't bring anything.
Others may chime in with more comprehensive recommendations.
Be safe out there,