Talking from experience, bring extra brake parts. Nothing ruins your day more than no brakes, it’s happened to me, and I’ve seen it happen to other people. I’ve offered my help, but since they didn’t have the same brand of kart I have, they packed it up and went home.
I always bring both of my karts incase something major happens to the kart I intend to drive. I’ve had brake cable break on first session, exhaust pipe crack, motor blow up, transmission blow up, crash with damage, ignition failure. All of these times, I was able to roll out my back up kart and continue the remainder of the day without any further issues.
I have a rollaway mounted in my trailer, all of my consumables are in that rollaway and never leave the trailer. When I use a part, I replace it before I go out again. If I break a part I don’t have, I buy 2 and have a spare for the next time.