Give a lot of gifts to one character and complete that game. Start a new game on that saved game file and choose to play as the character that received the gifts in the previous game. Those items will be available in your inventory in the new game.

Bonus songs

Successfully complete the game and save. Resume the game with the same saved game file to have two additional songs, "How Crazy Are You?" by Meja and "Is This Love?" by Bob Marley selectable under the Radio Station.

Swimsuits in exhibition mode

Earn or buy swimsuits in story mode (Zack's Island). The swimsuits that you acquire in that mode will also be available in exhibition mode.

Disable commentary

Enter the options menu, then change Zack's language to Japanese.

Ending bonus