For the most authentic MilSim game, you need MOLLE gear.
The MOLLE system was first introduced in 1997 by the United States Army Natick Soldier Research, Development and Engineering Center in Maryland, as a replacement for the old All-Purpose Lightweight Individual Carrying Equipement (ALICE) system that had been standard since 1973.
MOLLE is an acronym for Modular Lightweight Load-carrying Equipment, and is pronounced like the girl's name Molly. MOLLE uses Pouch Attachment Ladder System (PALS) webbing to allow for a modular approach to attaching pieces of gear by interlinking complementary nylon webbing.
MOLLE is technically a proprietary name, but is often used interchangeably to refer both to MOLLE gear and all PALS gear. PALS webbing can be found on a wide variety of gear types, including harnesses, vests, and gear bags. The purpose of PALS is to allow a paintballer to customize their loadout, letting them bring exactly what they need out onto the field with them- no more, and no less.