During gameplay press ~ (tilde) to go to console,  then enter the following cheats: 

ADDCASH - Get Some Cash 
NEXTMISSION - Complete Mission 
FAILMISSION - Fail Mission 
ROCK - Enable God Mode 
GOD - Enable God Mode 
GIMMEALLMISSIONS - Enable Cruise Mode 
FREECAM - Enable Fly Mode 
JUMP - Press Left Shift To Jump 
SPEED - Press Left Shift For Turbo Boost 
TELEPORT - Press R to Teleport To Random Locations 
CAMERAEDITOR - Show Cameras 
CARCAMEDIT - Move Camera 
SETLIGHT - Show Light Settings 
SHOWNODES - Show Nodes 
SHOWSOUNDS - Show Sound-Lines 
EXIT - Exit Game 
CANNON - ? 
MINIGUN - ? 
ROCKET - ? 
AMBIENTB - ? 
AMBIENTG - ? 
AMBIENTR - ? 
CARCAMSETATTACHED - ? 
CARCAMSETLERP - ? 
CARCAMSETVIEWCAR - ? 
CUTEPISODE - ? 
CUTMISSION - ? 
CUTMISSION - ? 
DIFFUSEB - ? 
DIFFUSEG - ? 
DIFFUSER - ? 
FLARESAVE - ? 
LENSFLARE - ? 
LIGHTEDIT - ? 
SAVECARCAM - ? 
SETINT - ? 
SETSTEPSIZE - ? 
SHOWRESPAWNS - ? 
SPECULARB - ? 
SPECULARG - ? 
SPECULARR - ? 


NOTE: This game is either very buggy or beta, for which reason 
some of the cheats may, or not, crash the game randomly.