If you're named "Jack" you have a huge selection of books. One of my favorites is Below by Nina Crews. Jack imagines that the stairs in his house are a mountain to climb or cities to explore. One day, Jack and his best friend/toy, Guy discover a hole in the stairs. Jack sends Guy in to get a closer look and he ends up getting stuck. Jack pictures various dangerous situations that Guy might find below the stairs and decides to rescue him. I love that Jack uses his imagination to transform the everyday into something magical. Gus, is Jack's younger brother, which is why it is tagged in this post.