During your run, enter the follow commands to first unlock the cheat codes:
UP, TRIANGLE, DOWN, X, LEFT, CIRCLE, RIGHT, SQUARE

A message saying "Cheats Unlocked" will flash on screen. This will last only for one race. You can then enter any of the following during your run:

Anti-Gravity: DOWN, TRIANGLE, SQUARE, SQUARE, UP
Super Bunny Hop: UP, X, LEFT, SQUARE, UP
Super Bounce: LEFT, SQUARE, X, UP, TRIANGLE
Mega Flip: RIGHT, UP, UP, RIGHT, RIGHT, SQUARE
Adrenaline Boost: DOWN, LEFT, LEFT, RIGHT
Combat Upgrade: UP, DOWN, LEFT, LEFT, RIGHT
Stoke Trick Meter: DOWN, LEFT, LEFT, RIGHT, RIGHT
Upgrade to Bottle: UP, DOWN, LEFT, LEFT, RIGHT, RIGHT
Energy Restore: DOWN, RIGHT, RIGHT, LEFT, LEFT
Always Stoked: DOWN, SQUARE, SQUARE, LEFT, CIRCLE
No Combat: LEFT, SQUARE, CIRCLE, SQUARE, LEFT
Extra Smack Time: LEFT, RIGHT, DOWN, DOWN
Infinite Bottles: UP, X, LEFT, LEFT, CIRCLE, CIRCLE
More $$$: RIGHT, UP, UP, CIRCLE, CIRCLE, SQUARE
Speed Freak: DOWN, TRIANGLE, RIGHT, RIGHT, SQUARE
Unlimited Energy: DOWN, TRIANGLE, LEFT, LEFT, SQUARE

During gameplay, pause, hold L1 and R1, and then press CIRCLE, X, CIRCLE. Next, release all buttons and then press SQUARE. Now press R1 and TRIANGLE together, and there should be a message saying you have unlocked all the bonuses in the game.

Play arcade mode with two people/controllers. Finish the race with only one player, leaving the other player at the starting line. Until player 2 finsihes the race, the race continues.

Use the first player to hit all the opponents that have already passed the line. Player one cannot finish first, as that prevents him from moving around to hit other racers.