Batteries, get 2 or 3. Never know how much shooting you might do in a game, some games, a few hundred rounds, others, a few thousand.
Utility pouch is something very useful, carries extra batteries, some small multi tools, food, ect.
You wont truely ever know what you need and what you will use, til you get out and play a few games. Keep things bare minimum for awhile, and then learn your style and needs and then tailor your gear to that.