After collecting everything in the game, two item slots remain empty - the Magic Cape and Book of Mudora, while coded into the game and fill these slots when hacked into the player's inventory, cannot be obtained normally.

The Magic Cape works as usual (you become invisible and invincible at the cost of magic power), but the Book of Mudora does nothing; as it fills the last slot in the A-button portion of the status screen, you were likely supposed to find the Book and either use it yourself (as in ALTTP) or give it to Zelda.