A jumbo bag of Every Flavour Beans, a caramel apple, a brand new~ copy of the Quidditch Cuties 1998 calendar, featuring shirtless Quidditch players (Zacharias is such a good friend, he knows), and a slip of paper that says "IOU alcohol".
Also, the following note:
Susan,
Happy Halloween. I'll have you know it was a pain to think of something to give you with your birthday coming up.
Love you etc.
Tirzah was instructed to wait until Susan was asleep but might not have been successful. She also charmed the paper BRIGHT PINK, and when it opens, it sheds rainbow glitter. This was not a part of Zacharias's instructions.