Most import...a healthy sense of humor and total lack of personal dignity.
But seriously, not covered because this was about stuff and not people. Stuff is easy. You can borrow or buy stuff you forget. People are hard.
If you have not attended a race and if your teammates have not, try to. If not possible understand all of the following:
When things break, they will not be what you planned for.
The same thing you fixed before coming to race preemptively, may be what breaks.
When things break, you will find plenty of help fixing it if you ask (we send folks in both directions of paddock if one of our main teams does not have something) BUT people will also mock you in a very good hearted way
If you do something supremely stupid, most teams have no problem telling you so...but they may be wearing pig slippers and Superman underoos on the outside at the time
Everyone takes track safety seriously...but almost nothing else...embrace this attitude and you will enjoy yourself more.
And this goes for all your teammates, hangers-on, feral children and domesticate wolves.
All of the above advice, and especially what OnkelUdo said.
Be friendly and helpful to other teams, and the good karma will pay off when you need it.
Bring your basics, but don't be afraid to ask around for the crap you didn't bring: tools, parts, or just about anything else. Teams will normally loan any needed tool or part, unless their car is in imminent need, like on its way back to the paddock on the tow truck. We've loaned out an engine hoist at Barber and Atlanta and not seen it again until midafternoon Sunday after it passed through two or three teams over the weekend. We've loaned/given spare wheel lug bolts, fuel line, odd sized hose clamps, power steering fluid, oil, gas, and special tools. Offered our spare clutch once on a "mail me a check next week" basis, but the other Beetle team decided that the odds of getting it in before the race ended was way too low. We offered to help them change it out since we've done a couple of Beetle clutches, but they decided to start drinking beer and load up early instead. We've borrowed an equivalent list of stuff from other teams. Send tool/part searchers in two or three directions, and hit all the teams running similar vehicles for special tools like triple-box wrenches for VW/Audi/Porsche. Everything loaned out has shown back up so far, even when it was loaned to some random guy in a red t-shirt who ran up asking if we had whatever it was they desperately needed and we forgot what team he said it was right after he left. We've gotten great advice from other teams, too; and been able to offer suggestions a time or two as well.
Oh, and for a brand new team - find a friendly but experienced team to paddock next to for your first race or two; and watch, listen, and learn.