* What would you do if your buddy kicked your reg out of your mouth?
Action: I would breath out slowly and get it back. If I had a hard time finding it, I would use my secondary until I found it.
Prevention: Try to avoid swimming near my buddy's fins. Either next to them, or if not possible, keep enough distance so my buddy can fin easily and not hit me.
* What would you do if your mask strap broke and you lost your mask?
Action: Get my buddy's attention and ascend. If it is fresh water I can swim up fine myself, if salt, I would hang on to them.
Prevention: Keep a spare with me just in case is the only prevention I can think of. Inspect the strap before the dive to make it less likely.
* What would you do if a fin strap broke during your dive?
Action: I have spring straps, so in theory that should never happen. However if it did, my fins sink. If I couldn't get it before it got away from me, I would use breathing and my BC if needed to ascend safely.
Prevention: Kinda did that by buying spring straps and I keep them rinsed and inspect them every dive.
* What would you do if your inflator/dump valve pulled out of your BC?
Action: Depends which one and what I am doing I suppose. If I am trying to let air out, I would adjust my position and pull a different valve to let air out. I have 3 places to release air. If I was trying to inflate and the inflater pulled out, assuming I could not manually inflate, I would drop some weights until I was neutral and ascend safely. If needed, I would drop a couple more at the surface to get positive. If I was using a dry suit, I would inflate the suit to adjust for the BC taking water or not having air if I need it.
Prevention: Have my BC serviced every year and inspect it before a dive to make sure nothing seems worn or questionable.
* What would you do if your only light went out on a night dive?
Action: Make a noise to alert my buddy and ascend. End the dive.
Prevention: I don't dive with one light at night. I keep a main light, a backup/peek in small holes light, and a tank beacon.
This all sounds reasonable. Let me know if there are better actions/preventions.