I take a spare Bass, a set of strings, fuses, batteries and a few spare leads.
I draw the line at a spare amp.
I have only ever broken 2 strings. One in rehearsal and one on stage.
It was a case of hit the mute button, unplug lead, take off bass, put on spare bass, plug in, hit mute button and play on.
Must've taken all of 10 seconds.