Master Cheat:
Go to the character selection screen and HOLD all these buttons together on controllers #1 and # 4: L + R + Left Analog-stick + Right Analog-stick + X + Y
 

Get Expert Mode:
Go to the character selection screen and HOLD Black + White and press A. If done correctly it will say 'expert' in the lower left of the screen. In this mode no arrows or stop indicators are on screen

Disable Arrows:
Go to the character selection screen and HOLD White and press A. If done correctly it will say 'no arrows' in the lower left of the screen.

Disable Destination Indicator:
Go to the character selection screen and HOLD Black and press A. If done correctly it will say 'no destination mark' in the lower left of the screen.

Get Another Day Mode:
Finish level 3 using Crazy X mode to unlock Another Day Mode

Get All Drivers:
Use Crazy X mode and finish level S-S

Get West Coast, Small Apple & Glitter Oasis Maps:
Use Crazy X mode and finish Level 1

Get More Vehicles:
Use Crazy X mode to finish Level 2 and you get a stroller, bike and carriage

Surviving the crazy-x football:
To help you beat the Crazy X football part jump over the big semi's and the big crowd of small cars. after you avoid the semi's it's just crusin' for you.

(Jump is the Y button)