Shoes!!
Maybe even two pairs, in case one breaks.
Depending on the weather where you are, I’d take a warm coat for after the race - easy to get cold when you’re tired.
I’d take a tube or two, even if you’re tubeless. And if you’re tubeless, take tyre plugs. If you have space for spares, gear/brake cables are easy to carry, and maybe a spoke? Depends how easy it is for you to fix your bike, how easy it is to get to a shop, and if you’d want to save at least your second race, if you have a mechanical in the first.