There are several items that I cannot live with when I go to a game.
1) Guns, mags, batteries and bbs
5) Mask of some sort
6) Elbow and knee pads - if I didn't have these I would have bruises everywhere
7) A hat - so I don't get shot in the back of the head
As for everything else, you can get it over the time you play. BDUs are pretty much mandatory, but you still game without one. I still bought one though when I started out.