Here's my awesome idea for how ammo crates should work:
1) Ammo crates can be deployed randomly or where the server host wants them.
2) Ammo crates don't let the players change weapons
3) Ammo crates start off full, but aren't an infinite ammo fountain, they have a limited number of EACH type of ammo: shells, rifle rounds, SMG rounds, and grenades.
4) Players can refill the crates.
..... A) Players refill crates by pressing a "dump ammo" key
..... B) Players can dump grenades or bullets, depending on whether they're holding a grenade or a gun.
..... C) As an incentive, the crate refills with 3x the amount of ammo the player is actually dropping
..... D) However, once ammo is dropped, the player can't take ammo from that crate until he respawns.
..... E) The player can only dump ammo that isn't currently loaded in their gun
This will add a new "supply line" element to the game. A handful of players can resupply a given crate, and help their whole team hold a strategic point.