Into the Wild is structured into chapters, with each chapter headed by quotes, diary entries, and postcards from Chris McCandless; these help define the themes of each chapter, as well as providing a better look into Chris's mind. The book itself is mainly composed of interviews with people who knew or met Chris, with Jon Krakauer acting as reader-surrogate and interviewer. The interviews are not presented as audio transcripts, but as conversations inside prose describing the countryside, the people, Krakauer's thoughts, and other pertinent information. This allows the somewhat dry Q/A style to flow easier for the reader. The book is straightforward non-fiction, with no invented elements; Krakauer also includes a story of his own experience climbing that he feels relates to the text, with the intention of humanizing Chris through his own shared obstacles.
On one hand, I'm tempted to say that Into the Wild is not organized at all. Or I might say that it's organized in a random and haphazard way. That's not true though. The book is organized. It's just not organized in a way that I liked a lot at the time that I read it.
The book is organized into chapters, and each chapter is entirely focused on a description of Chris McCandless in some fashion or capacity. The chapter might be focused on his wanderings through the Anza-Borrego desert in Southern California. Or the chapter might be focused on his declining relationship with his parents during his college years. Or the chapter might be about people that Krakauer believes were similar to McCandless for one reason or another. Each chapter, by itself, is great. Very well written prose, and I see a point to each chapter.
My complaint about the organization is that the book does not follow a chronological story telling about McCandless. The book uses flashbacks quite frequently, and on some occasions would use a flashback within a flashback. It was never confusing, which is a tribute to Krakauer's writing ability, but I found it jarring to be pulled away from the wanderings of McCandless so often. I liked the chapters in which Krakauer compared several men to Chris, including Krakauer himself, but I found myself wishing that Krakauer would hurry up and get back to McCandless's "adventure." The jumping around organization of the book is likely the reason the movie went with a much more linear story telling style. It's more simply organized and more accessible to more audience members.