Pause the game, select "Options", "Extras", then "Enter Cheat Code". Enter one of the following codes to activate the corresponding cheat function:

Play as Isaac Clarke from Dead Space
Enter "deadspacetoo" as a code to unlock Isaac Clarke from Dead Space.
Hoverboard mode
Enter "mcfly" as a code. In this mode, trucks and wheels disappear from your board.
Mini-Skater mode
Enter "miniskaters" as a code.
Zombie mode
Enter "zombie" as a code. In this mode, the screen will turn yellow and pedestrians will chase you.
Reset all objects to their original positions
Enter "streetsweeper" as a code.

Play as Dem Bones
Successfully complete all Hall Of Meat challenges to unlock Dem Bones.