The current weapon pickup system is fine for lower difficulties, but can get a bit clunky on harder difficulties, where not being able to shoot for even a second can lead to getting surrounded and subsequently dying. Here’s minor tweaks that could improve gameplay.
Weapon pickup into alternate slot: A separate keybind that would let you equip a weapon pickup into your alternate weapon slot, not your current one. Often, you won’t pick up a weapon to use it immediately, but you’ll save it for later once the ammo on your stronger weapon runs out, or for a more appropriate situation (i.e. melee). Unfortunately, this is less viable on harder difficulties, since the gap in shooting while switching weapons, picking the new weapon up, and switching back can make it much easier for zombies to catch up to you. Being able to pick a weapon up into your alternate slot would fix this.
Dropping weapons: Fairly straightforward, a keybind that would dispose of your current weapon pickup and immediately switch back to your starter weapon. Useful for accidental pickups in the later game, where many weapon pickups are much worse than things like the uzis or dual pistols, but also useful if you have two melees equipped and suddenly need a ranged weapon.