I swap guitars at gigs. Acoustic to electric and back again. It doesn;t take long, so don't worry about it.
Basswise, I always carry a spare bass. One night about 10 years ago, one coil of my trusty old P bass died. That left me open circuit and with (almost) no sound at all. There was a very little faint sound with some hiss. So we went into the PA aswell. Turned evrything up , knocked off the treble to remove the hiss and battled to the end.
The chances of that happening again are slim but I'm not prepared to take that chance.
On Sunday I have a Police gig and will appear as a modern Sting which means my '57 Bravewood replica, but I'll take the 70's fretless re-issue just in case of any problems. When I do late 70's Sting I have the Ibanez Musician fretless as the back up to the fender!! (lovely)