Trip did a good job of covering the basics. Couple other things that may help.

1. a set of bark busters/hand guards on your bike. There will be stuff wacking you on the hands from time to time.
2. a set of bib mousses rather than tubes in your tires can save you a flat tire out on the course. If not bibs at least running heavy duty tubes with sealant in them will help. There's no shortage of thorns out there.
3. bring some armor: helmet, goggles and boots for sure. a chest protector, knee guards and elbow guards will help in case of an unexpected get off or close encounter with a tree.