I imagine it like this:

1st: Character has two more slots. First new slot is for Secondary Weapon: there should be a legholster for the pistol/shorty. Second new slot is for a short melee weapon. This could be a sheath on the hip.
Now if you press the assigned button for Secondary, the Character draws the secondary/short melee from the new holster/sheath. (this would look very cool)
Additionally, there should be new knife animations. Knives should be able to hold in two directions (with different gameplay effects)

2nd: Fast weapon switching: if you press the quickbutton for your melee or secondary twice, the character should just dropped the weapon/item he is currently holding and took the selected weapon faster in his hands. This could be very useful if your gun is empty in fights and you have to switch fast to your secondary. Of course, the dropped weapon/item would land on the ground and you'd have to pick it up again.