Minimum that you need is really just the gun, ammo, battery, charger, eye protection, decent footwear and a hi-cap mag.
A basic load-out of gear would include the above as well as camo (either basic OD or tan, or fancier digital patterns like CADPAT OR MARPAT), a vest or chest rig (+ pouches if it's a molle rig), a sling and a carry case for your rifle, some sort of wearable hydration system (camelbak or just a basic belt canteen) and replace the hi-cap mag with a load of real/low/mid-cap mags.
A full load-out would include the above as well as shooting gloves, knee-pads (possibly elbow-pads as well), duty belt, drop pouch, a spare battery, and a decent ruck to carry it all to and from the game.
A full load out plus would include the above as well as a radio + pouch, and a sidearm + holster + gas adapter. Eventually a cqb/backup/loaner weapon as well, with batteries and mags to go with it, and maybe a few grenades.
At some point you're probably going to want to add some sort of optics to your rifle as well. For that I recommend a decent red dot sight, and use a carry handle rail for ease of use.