It could have turned out to be a great volunteering scheme and I end up with a lot of experience and contacts in the industry. On the other hand, it could turn out terrible and i'd be stuck out of sight washing the dishes every day.
True. But you quit after a single shift, done on a day which was by no means a normal day. You didn't even give it a second chance. So you'll never know how it would've turned out.
Heck, I don't see anything that indicates you even talked it over with the manager. He might have given you a more realistic view of the job and the future.
I think that's what annoyed most of the posters on this thread. Not the fact that you made a decision one way or another, but the fact that you started whining about it so quickly, without giving it a few days/shifts to see how it would turn out.
It was certainly my reason for getting involved with this thread.