Control logo
Press the [Analog-stick] or [D-pad] at the title screen to rotate the game's logo.
Millennium countdown
Successfully complete the game and allow the credits to end. Press A to display a black screen with a countdown to the year 2000. Note: The countdown still progresses even after the year 2000 has passed.
Unlimited grenades, shotgun shells, and first aid sprays
When you leave the last cabin on Disc 4 you will find two grenades, shotgun shells, and various first aid sprays in the snow. Pick these up, then re-enter the cabin. Go back outside and all the items will be there again. Note: This also works by saving than restarting your file in any place on the last path.