Eye pro is a must. Of course that's a givin.
Camo is highly encouraged for team placement, or you can stick out like a sore thumb all day.
Boots are very highly recommended. Rough terrain. Keep in mind you come out to play at your own risk. If you get injured, no one else is liable besides you.
Bring plenty of water, BBs, and a good attitude and expect a good day of airsoft.