What to do when you're stuck in an elevator.

wait for the generator to be switched on.

I think that I would just sit down and wait. The elevators in my building get stuck quite often (they are updating them now). There isn't much else a person can do after you push the alarm button. If I had reading material, I would use that to pass the time. I would just hope that the elevator isn't packed because I would then get very claustrophobic.