[Con Murder]

To add to the real question of a PMC load out.
It is loaded with pouches as these men rely on what they have to get the job done. Military can rely on what the military has. Lots of mags with a STANAG firearm (get creative man, give a back story for your merc and his choice weapon) if you work for NATO and well get creative if you don't. The number of mags is staggering, like 10-14 so remember that molle is a must. Add grenade pouches and fill with a balance of distraction devices and grenades, 40mm grenades if you got them.
Remember that these people hit hard and have to get in and out all with out resuply. Take that into your role in airsoft, playing as a PMC? Fill up on ammo at the start of the day and don't reload. Takes the role to a new level.
As for looking the part on the airsoft field, you gotta convince your friends nothing more. If they are CODM2 freaks you can probably go jeans a T and your tac rig. If they are a CADPAT clad team maybe rock the pants or a hat in CADPAT. Your still on a team and trying to make it easy for your teammates to tell friend from fiend helps everyone. Your choice of camo should be blend of where you are and where your from, if your team is in desert colors you could use DPM pants with a tan T shirt as a British pmc. Or OD shirt with Alpenflage plants if your a Swede on say a Woodland team.

Small things can help with your BDU looking custom. Have a lady friend customize some stichting for you or put in mesh (armpits and crotch). The collars and the pockets can be altered to prefrance, remember under a vest you can't reach breast pockets. Get some character specific extras to fill out loose ends and make it convincing. A German pin or union jack bandana can say alot with out being drastic. A novel watch or glove set can help set you apart, along with eyewear and head gear. Remember it can all be customized to look like it was made for you as a pmc, but airsoft is a team sport so try plan as part of a team.