I'd add insulate/nomex/whatever gloves in case I had to do something around hot headers.
A few times I'd bring a 10x10 "easy-up", like for 2-day events in Summer.
Extra oil & ATF & gear lube, 5-gal water jug.
The "race" tool box, floor jack & stands, extra tie-downs, and a few spare parts.
I kept most everything in the truck or on the (open) trailer.
That means duplicate items, and so be it.
Rather have stuff I never needed, than need it & not have it.
Sometimes that would help someone else out.