Master Cheat:

At the main menu press Up, Right, Down, Left, Right, Right, Up, Down, Left, Right, Up, Left, Right, Right, Down, B.

All Bikes:

At the main menu press Up, Left, Down, Right, Down, Down, Right, Down, Down, Left, B.

Amish Boy:

At the main menu press Up, Left, Down, Right, Right, Left, Left, Down, Up ,Left, Down, B.

FMV Clips:

At the main menu press Up, Left, Down, Right, Left, Left, Right, Left Up, Down, B.

Mike Dias:

At the main menu press Up, Left, Down, Right, Right, Left, Up, Down, Up, Right, B.

Park Editor Items:

At the main menu press Up, Left, Down, Right, Down, Up, Up, Down, Right, Right, B.

Park Editor Themes:

At the main menu press Up, Left, Down, Right, Down, Up, Right, Left, Left, B.