To drive anywhere on the track, go to Set Options, then press Down, Left, Up, Right, Down, Right, Up, Left, Right, Left.
Inferno in VS Mode
To unlock this planet in VS Mode, go to Change Planets and press Up, Right, Up, Right, Down, Left, Down, Left, Right. Inferno will now be available to select.
Infinite Bullets
For infinite bullets, enter the Buy Equipment screen, then press Down, Down, Down, Up, Down, Left, Right, Left, Down.
Infinite Money
At the main screen showing your racing stats, driver, money etc. Press Up, Right, Down, Left, Up, Left, Down, Right, Up. $250,000 will be added to your cash. You can do this as many times as you want.
Olaf
To unlock Olaf, at the character select screen, press Up, Right, Up, Right, Down, Left, Down, Left, Right.