Inside the new copies of No Such Thing as a Witch and What the Witch Left, I saw that there were not one but two e-book omnibuses being promoted.
The second one, which I assume is going to be released with the next two paper-and-ink books in January 2014, is called Three Wishing Tales, and will contain The Wishing Tree, The Magic Coin, and The Magic Cave.
Random House has some more information available here: