Press Ctrl + Alt + ~ and enter one of the following codes:
God mode: god
Full weapons and ammunition: give all
Full ammunition for current weapons: give ammo
Armor to 125: give armor
Classic 1995 version: give doom95
Health to 100: give health
All keys: give keys
BFG: give weapon_bfg
Chainsaw: give weapon_chainsaw
Machine gun: give weapon_machinegun
Plasmagun: give weapon_plasmagun
Rocket launcher: give weapon_rocketlauncher
Shotgun: give weapon_shotgun
Spawn indicated item: give [item name]
Play indicated map: map [map name]