I wasn’t as prepared as I should have been and decided to create a checklist
Do you use a checklist?

Please feel free to add on

Checklist for race car

Computer
Notebook binder
Pencil


Gasoline
Race gas additive
Race gas tank
Transmission fluid

Race suit
Helmet
Roll cage, sidebar

Windownet
Engine, Diaper
Water for rad

Tool case 1
Heat gun
Impact gun with sockets
Spare tires and lug nuts
Air pig
Generator
Cooling fan

Food
Chair
Water
Cooler
Suntan lotion
Hat
T-shirt
Tent

Check prior to loading
Test voltage
Lug nuts torque
Fuel level
Rad level

Prayers

Large amount of cash!

If you have an enclosed trailer, make sure the car is in it....

I forget my checklist. Birdtracker

Jack and Jack stands or that spare tire and impact gun won’t do you any good 👍
Also check trailer tire pressures

Define "large".

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.

I use a checklist app on my phone. Either ever note or keep notes. I use voice to text to create the checklists so that I don't need to type anything. Then anytime, anywhere, if something pops into my head that I should add to the list, I can just get my phone out and add it. Both of these apps have a an option to use a checkbox in front of every item. So when I'm packing, I can just check the boxes.
I can copy and paste a checklist from a prior trip into a new note and modify it if needed. It's pretty handy

after i tore my pants from the hip to the knee i started packing extra clothes and shoes

I retired from racing this year, and sold everything. Since I had an open trailer and my pickup truck was my daily driver, I had to load/unload everything each trip to the track.
I had a tote that had engine gaskets, oil, filter, ATF, brake cleaner, other fluids.
Another tote had spare starter, fuel pump, pushrods, spark plugs.
2-drawer tool box with hand tools, a plastic box with all carb parts and gaskets, another plastic box with electrical wire, connectors, zip ties.
Generator, battery charger, extension cord, 2 fully-charged jump boxes.
For a Saturday night race, a 10 X 14 cooler was sufficient. A weekend race requires another large cooler full of ice.

I gave the two track-day totes to the guy that bought the car.

I always check the tire pressures on the tow rig and trailer before load the car.

All of it

Touche!

Practice tree
Weather station
Snacks
Every carb tuning part made
Good led lights for needed repairs
Way more alcohol than I could ever use
Generator gas
Rags,wax,cleaners
Air compressor and long line
Radiator sealers
I have a plastic box I call my lucky box with almost every size NF and NC grade 8 bolt I may need
Loc-tite
And of course a nice selection of tools, floor Jack etc.

Double check the tie downs/straps, to make sure your car is properly strapped down on the trailer, before leaving. Bring extra straps with you. Make sure trailer lights are functioning.

And transmission in park......Seen a guy forgot to put it in park and almost lost it

Timing light in that tool box?

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.