If you haven't tried this book you are missing out! I love that the cover feels like cardboard AND that when I read to a group of students they went to class to make a book for the library entitled Not a Shelf Marker.
From the Publisher: A box is just a box . . . unless it's not a box. From mountain to rocket ship, a small rabbit shows that a box will go as far as the imagination allows. Inspired by a memory of sitting in a box on her driveway with her sister, Antoinette Portis captures the thrill when pretend feels so real that it actually becomes real-when the imagination takes over and inside a cardboard box, a child is transported to a world where anything is possible.