I usually start with books advertised in monthly Scholastic Book Club fliers. There are many dollar deals each month for all grade levels. All you need to do to join the book club is work in education and create an account which is free.
To make the book kit I usually start with an overlay using a Boardmaker template. My overlay contains characters and key objects in the story. I then go looking for other materials many of which are free online such as character cut outs and sequencing cards.
The graphic organizer comes from a Scholastic book called "Reading Response Road Maps." The book which contains graphic organizers for 50 children's books for grades K-2 is currently on sale in e-book form at the Scholastic Teacher store website. Many of the books are commonly found in a school or local Library.
Book kits are an easy way to target multiple goals in therapy and when put in a plastic pouch or folder it is a convenient way to store all the materials for a given book in one place.