There's always that time when you don't have the tool you need to make a repair at the track. Been doing this stuff for over 20 years and it happens all the time. Now that I'm older and not wanting to work as much as I used to, if it's broken, I load it and go back home. The basic stuff I keep is enough to change a tire on the trailer, or a bulb or basic wiring stuff to fix a light or trailer brakes. That's about it, though. A good item to keep with you is some bar's leaks for radiator leaks, some repair tape, gas, a quart of oil and maybe an oil filter, and a basic tool set to do real basic stuff. That's about it.
I used to get stressed about forgetting stuff to do a transmission overhaul at the track but I guess I grew up. Doesn't bother me to go back home, or at the least, ask another racer to borrow something. Some guys are jerks and dont' loan stuff out but I ain't that way, I've loaned almost everything I had to help other racers, and it's usually bit me in the butt in later rounds, but it don't matter. It's frustrating either way at first but you get over it.
Unless, of course, you've got John Force's budget and sponsorship; in that case, take a spare car and at least 3 of every major component. I'm just not that serious anymore.
Preinspection lasts all week for me. So does preparing mentally and eating right for a few days ahead of the race; then loading up on foods the night before because I don't eat much on race day. I go a little overboard on preparation of the vehicle and the tow rig but as far as taking every tool I own, forget it. If it's broken beyond a spark plug or a loose nut behind the wheel, it goes back home. Some of the heads up racers are so serious that they've got to take everything, including a 50 person starting line crew.....
'92GT, 427" and '93 "LXVO" coupe