XRAY - Model racing cars

Belts
The small (2mm?) grub screws so you can rebuild a driveshaft - I normally have two ready built in the pit box
Grease for above and loctite
Steering block
Rear upright
Shock diaphragms
C-hub - they are sided so two ( to be honest I do not think I have ever had one break)
Spare pack of the plastic roll bar holders. The number of times I have set droop and forgotten to tighten the roll bar holder screws
Maybe a spool outdrive - in 3 years I have broken one

I travel with much more than the above but I have never had to fix anything else. For a big meeting I think bearings would be useful - wheel bearings if nothing else.

Right on the membrane but the grub screws are 901302 3mm*2.5 - if you are using the standard the drive shafts; I should remember but cannot recall if the ECS driveshafts use the same size or smaller. It is worth having a pack of driveshaft pins too. Either 9080210 for the 9.8 with square ends or 305392 for the 10mm ones with flat spots. I prefer the latter but they are 5 times more expensive! And you can flat spot your own.