In chapter 23 of Rodman Philbrick's Freak the Mighty, Kevin gives Max a book with blank pages. Like Kevin's dictionary, the empty book is something which Max will be able to fill up with thoughts of his own. Kevin tells Max to fill the pages with "their adventures." Kevin knows that he is not going to live much longer, given his condition. Although Max does not want to face Kevin's inevitable death, Kevin admits that he will not have the time to do it himself. This leaves the task to Max alone.
Therefore, Kevin's gift to Max is a blank book in which he can write down all of the adventures Max and Kevin had together.