Press TILDE to display the console window, then enter the cheats during game play:

No clipping mode ... noclip
Spawn item ... give <1-200>

Items:
The weapons have a minimum and maximum of 1; ammunition is limited to 200 as maximum.

machete
colt45
machinegun
rifle
bazooka
greasegun
colt45ammo
machinegunammo
rifleammo
greasegunammo
bazookaammo
backpack
grenade
landmine
flamethrower
gasoline