In many years of gigging from garages to arenas, I've often brought all of these from your list *AND* had to use them, some many times - extra cables, strings (including for guitarists), picks (for guitarists), straps (yes, for guitarists), strap buttons, a spare amp head, DI box, a soldering iron and solder, tool box, hex wrench set, batteries, duct tape, tooth picks, potentiometers, output jacks, extension cords.
Add microphone, folding music stand, folding guitar/bass stand, drum tuning key and kick pedal to that list. Also a lighter, earplugs, flashlight and various batteries. A lot of musicians owe me a lot of favors for bailing them out. I can count on one hand the times *I* needed that stuff.
When having to transport it myself, I've brought a backup bass a few times and needed one never. I've had to bail out other bassists on bills a couple of times, because they were too clueless to maintain their gear or made the mistake of using strap "locks" (especially Schaller). I've also attended hundreds of gigs, most of them with bassists involved, and observed a bass issue exactly once. Dude had an active bass and no backup battery - a maintenance issue. He had no battery, and when one was leant to him he had no way to open the battery cover (needed a screwdriver).
A hand truck with cab and amp and bag with all of the above is easy to push around as a one-trip carry with a bass in a gig bag on your back. Nearly impossible as a single trip with two basses. Two basses in a double bag on your back, maybe. Gets heavy, and you've got to either clutter the stage with unnecessary "backup" gear or leave it backstage and risk it being liberated by someone. It's not necessary me, and I like to be self-reliant and do it all in one carry whenever possible. Not beating my chest, just adding perspective. Couldn't care less what others do.
Cabs blown - yes. Many. Amps blown, yes again many. All of them were new-ish "boutique" brands too, never a simple lead sled from decades ago with smoke and dried beer coating the innards.