I have not raced anything on a track for decades, but I have work pit crew a few times for friends (Leonard D. Scott H, etc) and found out along side them some simple items that kept them from running on time or just an extra precaution.

Spare battery. Twice this has happened. Once, it stopped holding a charge. 2nd time tire blew, went through aluminum tub and smack the race battery.

Cut away knife for interior harness/net, just in case.

Extra fire extinguishers.

Chillable bottle to keep in the car while waiting to race. Hot and thirsty is not fun when your strapped into a car and waiting a while to stage. If you have room, an ice chest just of ice. Gets pretty hot out there.

Extra trans/engine oil, if not some gaskets, hoses, clamps, filters, Duct tape.

Small spool of wiring/electrical tape, because you know, stuff happens.

Sponsor stickers. You would be surprised at how much opportunities there are for a little promotion of someone's product.

toilet paper. Many pot-o-potties run out at big events, and the walk of shame out of one is not fun.

if your running carb(s) maybe some jets if your a 'track tooner'.

Spare trailer wheel. You can have new tires on your trailer, does not mean you won't hit a random object getting there.

Extra set of 'cool down' clothes.

Friends. Yes, being with friends never hurt and if you can park/camp/hang with some will be a big help if needed.

Have fun racing out there.