The weapon sling and duct tape ideas are great.
To make it more realistic one should NEED to craft or find a weapon sling to be able to put the gun on your back. No sling = gun on the ground, to do other things.

Slings! We need to shed this 'magic velcro' nonsense. I don't care if it's easy to make one out of rags or rope, just put a lid on survivors lugging around 3+ guns.

First-

*duct tape. As in tape you would use to patch holes in ducts, not tape that quacks at you if you get too close. Sorry, but it was driving me insane.

Second-

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).

And agree, there should also be the ability to improvise a two-point sling for weapons using rope or rags or the like.

I also like the gun case idea, I'm just not sold on the "it can absorb two mosin rounds" idea, as most anything would be destroyed after absorbing a 7.62x54r bullet, much less two. Nor on the whole "it can carry three guns" point. I think it would be cool to have A GUN (one) and its' accessories in a gun case, and then be allowed to fit that gun case in a mountain pack or to be carried by hand/stored in a tent or vehicle.

Duct tape can already be used to repair/fortify a number of items, as well as be used as makeshift handcuffs. I do like the idea of using duct tape to tape somebody's mouth shut - it would disable their in-game comms, and if they tried to talk it would come out as "mmmrmph, mmmph!", or some other muffled sounds.

Well, sorry to drive you insane a little more: https://tw-projects.s3.amazonaws.com/twduckbrand/prod/images/products/8daea9acef7a8e5b97f6015c1519d8f02b5d1437.jpg

I do like the ideas but not as an addition but rather as a replacement for the current magic slots. Crafting slings from not too rare items would make it a little more difficult to carry a rifle early but not cripple players too much. Though I would prefer if they added snap hooks for this purpose (and other applications). Or both of course with the taped one degrading over time.

That picture makes me want to rage poop. I am aware that "Duck Tape" is a brand. A brand of what, you may ask? Oh, right - DUCT tape.

And yeah, the magic slots gotta go. Snap hooks or D-rings or carabiners would be a pretty good idea. Shit, if you had carabiners, rope, ice axes and stakes you could go rock climbing, or rappelling.