Don't have one, really, though there are several bikes hanging around that I could ride, none of them are really equipped, they're family member's noodlin' around bikes, no lights, etc.

The only time I've ever had something break on my bike that I couldn't fix in time to ride was a couple of weeks ago when I broke an axle. Then I transferred all my stuff (fenders/racks/etc) to my wife's bike for 3 days while the new wheel came in, then moved everything back.

I could have just driven my car though. Did, for one day.