I've broken strings quite a few times at gigs, with no spare guitar. I just play to the end of the song and replace the string. It doesn't make me want to take a spare guitar, but it does mean that you have to use a guitar that will survive a string break without going wildly out of tune. (So no fully-floating trems that can't be locked.) If you know what to do and have the spare strings and tools to hand you can change a string in 30 seconds, so it really isn't a big hold-up, and I don't play the sort of gigs where slick polished performance matters... I think that at the type of gigs almost all of us are playing, it's unnecessary anyway.
I may be going off on a bit of a tangent here, but I find the whole "rock stars in a small pub" thing quite ridiculous. I'd far rather see some musicians just playing *live*, with all the compromises and randomness that can cause - including using the "wrong" sounds, having to interact with the crowd while Slow Hand on guitar changes a string for the third time (that's how Eric got his name, by the way...

), making mistakes and just generally being entertaining, than taking themselves far too seriously and acting like they're on Jools Holland. Different if you're in a name band at a proper venue gig of course - but even then, I find the whole touring-with-a-guitar-shop thing quite annoying. You don't see musicians other than guitarists needing to take half a dozen different instruments on stage with them. (OK, keyboard players in the old days sometimes did, but they were often ridiculed for it too.)
Or maybe I'm just a grumpy old fart

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