This trick requires two PSPs and two copies of the game. Select the item to be duplicated and trade it to another PSP. Do not save on your PSP but save on the other one. When you reload, because you did not save you will still have the item. However, because the other PSP saved with the item on it, they will also have the item.

Connect to a multi-player game. Have the character with the item give it to another player and do not save the game when exiting. The player who receives the items needs to save the game. When both players reload the game, they will both have the item.