Instructions
Go to the store in the game. The shopkeeper will ask you if you would like to shop in the store. Reply "Yes." The shopping list will then appear.
Look through the shopping list until you find the "Booster Pack Menu." Open the "Booster Pack Menu."
Press the following code with the controller buttons while in the "Booster Pack Menu": up two times, down two times, left, right, left, right, X and O.