I'll preface this by acknowledging that this thread is dead beyond all resuscitative measures, but it is kind of an interesting topic and I'm rather bored.
I actually attended a CE lecture on this exact topic ("Medicine at 30,000 Feet" or something to that regard) and found it pretty fascinating. The take home points I gathered are as followed:
1. Generally, the flight attendant/possibly captain may ask if there is a physician, nurse, or other provider on board.
2. They'll give you some sort of fly-by-night ramshackle bag filled with various odds and ends, most of them useless in nature. (Think IV tubing, oxygen tubing, and BP cuffs that are literally disintegrating due to lack of maintenance coupled with extreme temperature and pressure changes)
3. They're required to have some degree of oxygen available, but it's strictly regulated since it's a pressurized gas, and historically pressurized gases don't bode well on pressurized aircraft.
4. There is a strong possibility they will ask you for credentials before allowing you to go all Dr. Sky Cowboy on their passenger(s).
5. They can essentially tell you, "Thanks, but no thanks" if you've been drinking/had the standard pre-flight Valium.
6. Your main function is to triage, and tell the captain whether or not you recommend diversion to a closer airport (they're also more than capable of telling you, "thanks, but no thanks" at this point as well)
7. The FAA really only cares about them having the basics, whether they are in working order/non-expired medications is a whole other matter.
And finally, and most importantly:
8. You may be compensated in money from the airline, x,000 free flight miles, free peanuts or delicious Biscotti cookies, or something of absolutely zero value. There is no balanced billing on Delta, sadly.
Sorry if any/all of this was covered above, as I didn't exactly click the link.