One fairly important note - ALL Zone 8 Competition Rules apply as to Safety (unless explicitly modified by the AX/Safety Chairs for this event, which is unlikely). For the full rules, see
http://zone8.pca.org/rules.htm
(A little thing called "Event Insurance" means we all have to follow the rules...)
Regarding the "shifter cart" comment above -
XIV Safety Considerations, part M, says:
"All parts of the tire which normally contact the road must be covered by the fender when measured from a vertical drop from the fender edge through the center line of the wheel."
I.e., no carts or other "open wheel" vehicles (or ones with partial fenders over the tops). Sorry - you can't bring your BMW Sauber F1 to play.
Also, the usual noise limits at the Stadium apply, so any vehicles with straight pipes or other open exhausts aren't likely to be allowed.
In general, any automobile that you could purchase from a dealer and register for normal (and legal!) use on public highways "should" be ok (subject to tech and safety assessments). Vehicles with a high center of gravity are obviously discouraged due to rollover risks, and if you are thinking about bringing something particularly exotic, you should read (and understand) at least the Safety section of the Rules before showing up and being told you won't be allowed to run.