The deer is an interesting image.  Prior to the deer's entrance, the conception of identity we are presented is a shared notion.  In other words, everything is about the boys.  Their travels, the coin toss, running away from Chopper, walking to find the body, getting attacked by the beavers, and the stories are all about all of them.  Even their personal experiences are shared, as they all know everything about one another.  The deer is the first moment where the story is actually about Gordie. No one else experiences it and he doesn't tell anyone else about it.  This might represent an aspect of individual freedom, something that he alone will experience that no one else will.  When you examine how King describes it and how Gordie interprets it, pay attention to how this isolates him from everyone else.