Enter the "Edit Profile" screen. Choose 'Unlock Items' and select "Cheat Codes." Now enter the following codes:

IGIVEUP - Unlock everything
SHOWROOM - All ATVs
GAMEON - All minigames unlocked
TRLBLAZR - All tracks
THREADS - All equipment
GOLDCUPS - All championship events
GIMMEPTS - 1000 profile points
GABRIEL - Unlock San Jacinto Isles
FLYPAPER - Wrecks disabled/enabled
EATDIRT - Aggressive AI enabled/disabled