During the game drop the dev-console via the tilde key (left of the numeric row) and input the following code effect:

ALLAMMO ... Stock 999 rounds for current weapon.
AXE ... Use fire axe.
GLOCK ... Use handgun.
MINIGUN ... Use minigun.
MOLOTOV ... Use molotov cocktail.
SNIPER ... Use sniper rifle.
SHOTGUN ... Use shotgun.
WEAPONS ... Stock all weapons.
KUNGFU ... Use bare hands.
GOD ... Player invulnerability.
GHOST ... No clipping mode.
FLY ... Free floating mode.
WALK ... Disable clipping and float modes.
BEHINDVIEW <0/1> ... Binary toggle for external view.