I'm pretty sure the skirmish type games dont have any sort of requirements.
You can show up in jeans and a Tshirt if you want.
Whether you get other gear or not, ALWAYS get good quality eye protection and boots. Eye protection is mandatory, and the boots are really really worth it. Paintball masks cost anywhere from 10 to 80 bucks. Good boots cost 80 bucks or more. Dont skimp out on those two.
Other than that, you could show up at a game with a gun, charged battery and one or two 500 round hicap magazines and play
H&K G36c (KWA) / Glock 18c (TM) / Kimber LAPD SWAT Custom (TM) / Mossberg M500 (ACM)