Win tournaments in the various countries to unlock their corresponding arenas.
Hold L + Y and press Right(2), Left, Up(3), Down, Left at the main menu.
At the main menu, hold L and Y, and press Right x2, Left, Up x3, Down and Left. No sound will make, but go into Create Player and you will have all the kits.
Pause game play, then hold L + Y and press Up, Left, Down(2), Right, Down, Up, Left.
Pause game play, then hold L + Y and press Right(2), Up, Down(2), Left, Right, Left.