We do have a pretty unique procedure - if the bass rig craps out completely then one of the bari sax players swaps to playing the bass guitar parts and I go to the bar!
It hasn't happened yet, but it's like having a back up me!
But generally -
2 basses
2 amps
1 cab
di box (if there's a PA. No point if not!)
Always a spare guitar lead and Speakon speaker cable, battery, spare IEC power cable.
Pretty much everything other than the cab.