Unlock all tracks:
Press L1, R1, R2, Square, Circle in the main menu.

Unlock all cars:
Press L1, L2, R1, R2, Circle, Square in the main menu.

Unlock next cup:
Press L1, R1, R2, L2 in the main menu.

Fire backwards:
Hold R2 after hold Down while racing and fire.
Press Up to fire bouncing bombs forward

Unlock Vehicles, Tracks:
Unlock Big Rock - Win Gold Cup Championship
Unlock Concept 3000 - Beat the records for all Reverse Time Trials
Unlock Jungle Ranger - Win Silver Cup Championship
Unlock Level 2 Tracks - Win Bronze Cup Championship
Unlock Level 3 Tracks - Win Silver Cup Championship
Unlock Level 4 Tracks - Win Gold Cup Championship
Unlock Lunar Loader - Win Bronze Reverse Cup Championship
Unlock Sarge - Win Gold Reverse Cup Championship
Unlock Skull Duggery - Win Platinum Reverse Cup Championship
Unlock The Corporal - Win Bronze Cup Championship
Unlock UFO - Beat the records for all Normal Time Trials
Unlock Yella - Win Platinum Cup Championship
Unlock Zany Zoomer - Win Silver Reverse Cup Championship

Unlock modes:
Unlock Mirror mode - Win All Normal Championships
Unlock Reverse mode - Win All Reverse Championships