Hi,
I've been playing over 45 years and I will admit that is has occurred to me very rarely, only a few times in all those gigs. But it would have been an absolute disaster had I not had a backup with me.
Granted, when I was first starting out I could not afford a spare bass but as soon as I could I bought a second and brought both to my gigs. Even if you don't have a spare bass you should always have spare mic cables, speaker cables, instrument cables, etc. I have a strap for each bass, plus a spare. I usually carry four guitar stands with me, a pair of drum sticks, picks, extension cords, a couple of spare mics, maybe an extra mic stand, mic clips, and other paraphernalia (batteries) that could be forgotten by other bandmates. I just keep it all in my gig bag, just in case.
Thank you for your indulgence,
BassCliff