Hey Bill, I am organizing The 3rd Annual West Coast Chevelle Gathering (WCCG) and have turned down companies that keep offering me goody bags and bag stuffers. My theory is that as a participant, I never use coupons, discounts, or even really read anything in a goody bag. And as a guy who does care a little bit about just throwing everything away, I passed on goody bags and their contents. No joke, I have 2 goody bags full of stuff I'll never use or even look at in my Chevelle's trunk right now.
If you're going to spend the time and effort to contact companies (I've contacted about 125 companies for my event), ask for prizes or giveaways, not for goody bag stuffers.
If you really feel the need, contact all the sponsors you see on race cars, race tracks, and other car related events. That's what I did and I have a stellar prize list.
Good luck. You'll get about 33 no's to every yes!