Like Priest said there is a ton of topics.
Goggles (ballistic or paintball rated) are pretty much the standard thing. Most guys will run goggles and a mesh lower for things like CQB and usually just a shemagh, mouth guard or nothing for outdoor games and some will opt for full protection.
Most places require full seal goggles like ESS profiles, Revision Desert Locusts, and Smith OTW's just to name a few. There are some places the will require a paintball mask but it's not very common.
Durate et vosmet rebus servate secundis.