Unlimited items or gold
Find a location that contains multiple items or gold, such as the first room in Oedo Castle. Then, collect the items, leave the room, and re-enter. Now the items will be available for recollection.
Collect all 45 Fortune Dolls to unlock a boss mode selection on the options screen.
Enable the "Boss mode" code, and complete the Boss sequence.
When Impact's introduction sequence ends, press the Analog-stick to move his head.
Rumble Pak Bonus
Although not an official Rumble Pak game, the Boss levels will support the Rumble Pak.