Bonus parking levels:
Successfully complete each of the four parking levels to unlock an additional parking level. Successfully complete the bonus parking level to unlock a sixth parking level.

Nippon Maru:
Hold X and press Start at the title screen. Keep X held until the mode selection screen appears. Choose any mode to drive the Nippon Maru truck. Alternately, successfully complete arcade mode with all four characters:

Bonus trailers:
Successfully complete arcade mode with all four characters to unlock two bonus trailers in score attack mode, versus mode, and arcade mode (if the Nippon Maru is selected).