One other thing, if you don't mind the expense, is a slide stop. They do occasionally break. You gun will work, more than likely, with a broken ejector tip, cracked slide stop, etc. It won't work with a broken slide stop or extractor.
ETA: I did not post that to argue the point with skunkeye, since he is absolutely right. After reading it I thought it appeared I was being rather trollish. If you're going to be on the ultra safe side, having all these spare parts are nice. For the guy who mentioned just bringing a Glock, I've broken Glocks before too. As a matter of fact, I've broken more channel liners and spring cups in glocks than anything 1911 related. Again, I'm not trying to be arguementative, but all guns can break if used hard, and I think the guy who originally posted this is just one of those guys who plans ahead.