Honestly, there should be a variety of slings. Normal two-point slings that attach to each end of a rifle (all rifles/full-length shotguns, to sling over shoulder, or provide stability while shooting while standing), three-point slings that allow for you to carry the rifle in front of you (freeing up your back slot for another rifle or secondary melee weapon), one-point slings that can only be attached to certain vests (assault, smersh, hi-cap, plate carrier) and only certain guns (mp5k, m4, aks-74u, pistol-grip MP-133, RAK).

There should also be the ability to improvise a two-point sling for weapons using rope or the like.

One more thing I thought of was a variation of the gun holster. Why not make it so you can use it as a belt holster instead of just a chest holster? Somewhere to put a pistol other then in backpack or where ever everyone puts them.

Unless they add a sling for normal guns they should just let you put a second gun on your back. It shouldn't even have to be small though.

I love this idea! instead of the annoying 'carrying around another primary weapon in your hands as well as your back' making the weapon drop to the ground when you go to use your hands, it does not!

I hope this idea reaches to discussion sooner or later