I never took a backup to a gig exept when i was playing some songs and had to take my accoustic along - don't know if it counts. Allways took spare strings, batteries, tools, soldering equippment, contact cleaner spray... and never needed to use it with myself. Had to use it a lot of times with the guitarrist and once or twice with the drummer (i never heard of a drummer taking two kits to a gig, just in case...).
I have a lot of care with my gear and with each string change (every two or three months) i give my bass a good clean and a checkup.
Never broke a string in 12 years gigging, i'm very lighthanded.