Keeping everything glued together.
You might get away with just checking the oil and adding fuel for the first race or two, but eventually things start to wear out, break and fall off. A between-race prep ritual will mostly keep you on track rather than wrenching in the pit lane. Eventually something will fail on track and put a damper on your day, but you may as well eliminate as many variables as possible.
Opinions may vary, but I change engine oil and filter prior to each event, and gear oil over the winter. I use the highest viscosity synthetic engine oil that I can buy off the shelf, gear oil will depend on your application. Brake fluid will also vary by application, but after testing some obscenely expensive fluids, I found that off the shelf, high-temp DOT3 makes it through a race for us without any boiling or degradation. I do a full flush over the winter. Coolant by the rules is just water and Redline Water Wetter. Some will recommend distilled water, I’ve also read information to the contrary. Don’t forget to fill the system with antifreeze over the winter. Check all your fluid levels every time the car comes into the pits.
Bleed the brakes and clutch as part of your post race prep Saturday night, and again between weekends. If you are not sure how to do this, there are tutorials online to guide you through. A brake pedal going soft mid race is not a quick pit-stop fix, so take care of it before you get on track.
Check Brake Wear
Monitoring your brake pad consumption will highlight any abnormalities in the system that should be addressed before it causes a failure. Got a pad that is wearing faster than the rest? Maybe you have a sticky piston or seizing sliders. Have a look at those rotors too, cracking or discoloration might tell you it's time to rethink your brake ducting.
Nut and Bolt
At a minimum, I would recommend a nut and bolt check before every race weekend. We do a quick one on Saturday night as well. Put the car up on stands and grab yourself a handful of wrenches. If it helps, make a list, but go over all of your brake, suspension, drivetrain, steering, and safety equipment hardware to make sure nothing has come loose. Anything that can be held on with a lock nut or safety wire is a good preventative measure. Mark all your nuts and bolts with a paint pen or nail polish to add a quick visual inspection.
Bearings and Joints
With the car up in the air and the wheels on, give them a good wiggle in all directions. If you grab the tire at the top and bottom and feel play, you're probably losing a wheel bearing or ball joint. At the front end, if you have your hands on the front and rear of the tires and feel play, you could be losing a tie rod end. Give everything a good shake and figure it out before it goes bad on track.
Check your toe and camber after every race, especially if you've dropped a wheel off track or made contact with something. Poor alignment will slow you down and unnecessarily burn through your expensive tires.
This one is self explanatory. No point looking for more go fast goodies if your throttle cable has slipped/stretched and gone unnoticed. Have a guy push the pedal down to the floor while you make sure the throttle plate is all the way open.
Inspect Belts and Hoses
Make this part of your routine whenever you pop the hood to check the oil. Ensure nothing is rubbing or chafing. Check belt tension, loose belts will eventually become missing belts.
After each race make sure your air filter, rad duct and brake ducts aren't packed full of rubber, grass or dead animals. Seriously, I've pulled a bird out of our rad duct.
Don't forget to make sure all of your gadgets are charged and functioning properly. Radios, transponders, in-car timers etc. Bring them all back to the hotel/camper Saturday night and make sure everything is charged up and ready to go.
Make sure your fire bottle is charged. Check your harnesses for any wear or damage. Check your suit, gloves, helmet etc. for wear or damage. Before you head to the track, check expiry dates on your harnesses, window net, helmet, neck restraint.
Lights, Fans and Wipers
Especially important if there is a chance of rain. Make sure these items are all functioning as they should.
Wheels and tires
Torque your wheel nuts. Check for abnormal wear or damage to your tires. The night before the race, have all of your tire pressures a little on the high side, then bleed them in the morning to your cold settings. It's quicker and easier than fumbling around trying to add pressure in the morning when everyone else is gridding.
I hope if you made it this far, you've remembered to refuel.
There are maintenance items specific to each car that I haven't covered here, but these are the basic checks to get you through the weekend without anything falling off. If you are running cool suits and drinking systems, they will all need their own attention. The Thursday night before a race weekend is not a great time to start going over the car. Do as much as you can, as soon as you can. That way all those "it's probably good for another race" items will become "we've got time, we may as well fix it" items.
If you have any items to add, feel free to share and I’ll put them on my list.