What is the code of unlock items

I can't tell you because there is more than one and I don't have any to give away. Each code is different and can only be used once.
You can get exclusive items or money with them and what you can get/choose to get can be different
You can get codes by buying a piece of official Club Penguin merchandise that has the Unlock Items Online sign on it and is not a book.
There are also book codes where you have to type in the answer to a question about the book you have (e.g what is the second word on page 63, line 5?).