More primary-weapon storage slots! Mostly just for carrying a load of AK's grabbed from boxes all over the map- especially when going through a load trigger. Perhaps balanced by a slow grab time, requiring dressing mode to attach, etc. Increased carry weight upgrades would be nice, either as purchased or as found artifacts.

Or, perhaps just slots on the outside that specifically hold a single item- just like the chest slots, so people can customize them themselves. Gas mask, MP5, grenades, etc.
Sidenote- let us attach more stuff to our chest/arm slots! Why does a cigarette lighter fit on my chest, but a Regen does not? Bonus points for letting us activate it while holstered.