Seems no matter how much stuff you bring with you, there is always that one thing you forgot !!!
A flywheel puller is one thing a lot of people forget.. I keep one along with all my other standard tools for building/ maintenance
( within reason ) that stay in my tote tool box.
Spare pipes, cables, servos, switches, soldering iron, small torch, strut, rudder, turn fin...start belts, fuel tank, hose, coupler material, radio box tape, 200 mph racer tape...
I've mentioned this one before,, along
with my various glues and resin, I keep a piece of folded up fiberglass cloth and bag of cut off wood pieces, I keep a can of chopped fiberglass body filler/activator and a surform tool. This stuff is great for patching huge damage spots in hulls, putting blown apart sponsons back together etc.
It's much stronger than bondo, hardens quickly and using the surform tool you can shape it fast. The blade is like a cheese grater, and can be snapped into small pieces if necessary to fit into tight spaces.
I've fixed some major damage on hulls between rounds and didn't miss a heat.
Having a 6 in. sanding disk that fits a battery drill along with stick on sandpaper in different grits is a bonus to have with you also. I group a lot of items like these in softsided toolbags or a backpack and bring them along for races..not for a play day at the pond.