Motorcycle helmets work fine for DE (Driver Education) events, but if you want to do anything more serious you'll have to spend more money and buy a proper auto racing helmet. I would suggest renting a helmet, and use a head-sock. If you want to purchase a helmet, do not do it online, you have to try them on because they all fit differently.
Pretty much anything you'll need besides a helmet you can find by asking almost anyone at the track with you. You'll find that people will be very friendly and you'll have lots in common. Oh, and leave your ego at home.
