Pause the game and hold L, then press the following key combos to unlock the corresponding effect:
SUV: on the Enemies Vanquished level, press X, B, Y, X, Y
Extra Race: on the Enemies Vanquished level, press B, B, X, X, Y
Racing Trails: on any level, press X, B, B, X
3X Armor: on any level, press B, Y, X, B, B, B
2X Armor: on any level, press B, Y, X, B, B
4X Armor: on any level, press B, Y, X, B, B, B, B
Crazy Racing: on any level, press X, Y, B, Y, X
Insane Racing: on any level, press X, Y, Y, X, Y, B
Super Bullets: on any level, press B, B, B, B