There is much more to paintball than many people think. There are masks, gloves, jerseys, pods (holds extra paintballs), harnesses (holds pods) ,pants, hoppers (feed paint into gun), barrels, barrel stoppers (prevent balls to be shot in staging area) and even cleats! While only a few of these are absolutely necessary, each of them has it's purpose and some people even think all of them are needed to have a enjoyable game.
There are many different types of masks, but each has the same purpose though, to protect your face. But there are different levels of comfort so chose one that suits you best.
Protect your hands from paint balls so they don't get hurt.
These are the safety equipment items I feel are necessary no matter where you play.