You're not giving much to go on. Is this a GEAR load out or a COMPLETE load out (gun, mags, gear, ect.)? What is your load out, so that we can recommend things that match or at least compliment your load out? Where are you going to be playing mostly?
As far as my personal experience with "stealth", it's more about the player than the equipment. It's very easy to be "stealthy" when people are wearing masks or goggles that cover their ears. Tends to dampen noise very well. Footsteps tend to give be what gives people away, especially end playing in the forest or in a river bottom. Not much you can do about that. Rubber soled boots (or even Chuck Taylors) dampen footsteps indoors and outdoors, to a lesser extent.
Yes, midcaps do keep noise down, but polymer hicaps aren't excessively noisy. My G36 and SIG hicaps stay quiet unless I'm shaking the gun like a maraca. Those 400 round METAL G&G hicaps, on the other hand, sound like dinner bells. Another reason to consider polymer mags is your dump pouch. I've had times where I thought that the sound of my metal M14 mags in my dump pouch were broadcasting my location.
Speaking of metal clanking, don't go with a rail system and tape your sling swivels with some matte black or OD duct tape. Those things sound like give a distinct "ding" when they hit a rail system or the outer barrel of an M4. Polymer guns, like the G36 or UMP, are much more friendly as far as noise goes with one point slings.
As far as rigs go, obviously you don't want to have snap closures or velcro. Bungee cord retainers are your friend. This is a bigger deal in CQB than in the field, but it helps whenever you're close in with your opponents. Depending on the platform you're running, something like a Chi-Com Type 56 chest rig or a US LBV (with the top flaps tucked into the pouches or cut off) work great. Both are cheap as dirt, so you can modify and paint them to whatever camo scheme or preference you would like. If you have to have MOLLE, then Condor makes a nice chest rig that carries more M4 mags than you'll ever need, has a hydration carrier built in, and a decent amount of MOLLE for about $50. I haven't had any experience with it, but Condor also makes a rig called the "Ronin". It has enough MOLLE to attach some mag pouches and that's all. The main advantage is that you won't get weighed down with things you think you'll need.
Again, as I said up top, being sneaky is more of a skill than your equipment. Learn to use cover and concealment to avoid being spotted. Take the long way to get where you're going. Learn that you don't have to shoot every "bad guy" you see. Get into a good position with a good field of vision, decent cover, and an escape route before raising hell. It's 99% mental.
