Here is an interesting thing that happened to me;

We had a pretty big gig. It was more of a try out to get into a local club on a regular basis.
I recently picked up my dream amp (at the time)(Marshall JVM) so I was feeling good and felt no need for a back up.

Well about half was through the set my amp "went". No sound , nothing.

I was fortunate as a friend , who is also in a band was there and just happened to have his amp in the car.
Well that was a life saver.

And needless to say I do not travel without a backup anymore!