To insert the following codes, enable the console from the in-game options. Press ~ and type in "seta thereisacow 1337", pressing Enter thereafter. From here, type "spdevmap bog_a" and press Enter again. Then, you can insert the following cheats.

give (item) - Acquire any item
give all - Get any weapon
give ammo - Full ammo
god - God Mode (without screen shaking)