if you're just going to skirmish, I would go super light weight with emphasis on just going out for a shits and giggles good time... in that case, a few more high caps and a very light weight belt rig or chest rig to carry it is all you really need.
If you want to get more into milsim type games, you're going to have to outfit yourself with midcaps, the guys who milsim generally don't look kindly on winding highcaps. It's up to you how much you want to carry at that point, 10 mags? maybe more?
Be careful of what your pistol will chrono at you don't want your sidearm to shoot hotter than your rifle, as you'll be using it in closer. I'm not sure who makes that gun for g&g but it might not be the best choice (price and quality). Look at KJW pistols to see if you like something in there, something that runs on propane/green gas is far more suitable.
You're going to need something carry mags. Depending on how many mags, and depending on how heavy you want it, there's chest rigs, belts, vests, plate carriers... go check out army issue like danke said, nothing like being able to actually put it on and see how it fits.
Other things you may need:
Depending on the pistol, don't cheap out on the holster. I had nylon holsters drop mags out of my 226 twice, and had I not found the mags, I'd be out 80 bucks worth of mags. That loss along justified the expensive for a real steel serpa holster. It's by far the most favorite thing I've purchased. Super comfortable on my leg, doesn't move around, doesn't drop mags, and easy to draw from.
Water... how much and how you carry it is up to you. I generally carry a bottle of gatorade on my vest or belt in a radio pouch, and on my back I have around 1L of straight water in a camelbak or carrier integrated into my vest.
leave room for radio somewhere, you may not need one now, but keep it in mind.
I have an admin pouch to carry a bottle of bugspray, a couple simple tools, my kill rag, a couple cliff bars what have you.
While you don't need all real gear to play, some of it really is made to beat on and it'll take it without letting up. Other times it can be overkill, I mean do you really need to spend 80$ on a riggers belt that has a rating on it that can tow a truck when all you need is to keep your pants up?
I'm still running the condor vest I bought almost 3 years ago, and condor is probably on the lower end of what most people will buy, but some of my condor stuff is pretty low end, double pouches that were sewn with unequal sized pockets so mags wouldn't fit in one side, and too lose on the other.... silly stuff like that.
I futz with V2s, V3s and V6s. I could be wrong... but probably, most likely not, as far as I know.