Press "~" to enter console Mode then type the following codes:

Cheat Code - Granted Wish

give [weapon ammo] [amount] Give Ammo for Weapons

Weapon Ammo List:
(i.e. give Colt45Ammo 100)

machinegunammo
rifleammo
machinegun
rifle
bazookaammo
backpack
grenade
landmine
machete
colt45
bazooka
colt45ammo