Run out to target or somewhere and get some big plastic bins and maybe a tarp. Stuff that's well organized and covered isn't as likely to get snatched up. You could even talk to some of the organizers and see what their advice might be on where to keep some stuff. Usually paddok areas are pretty safe spots to leave a pile of tools and stuff when you're at a track, even if it is a parking lot. As long as you're around other car guys, make some friends and agree to look out for each other's stuff.
You've done so much and waited so long to get out on the track with a running car, don't let loosing some stuff stop ya
If you run into major problems, there's more than a few guys on here that can lend a hand, go have fun!