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 parking

Finish each of the four parking levels to unlock an additional parking level. Finish the bonus parking level to unlock a sixth parking level.

Unlock more parking levels

Finish the four parking levels to unlock a fifth parking level. If you finsih that as well, you will unlock a sixth parking level as well.