The book Into the Wild by John Krakaeur has a bias in it. Is that because of his trip to Mount Everest in a different book he wrote? And what are the most important chapters in the book? I thought it was 1, 5, 8 and 18 because it talked about family.
I do not think that Krakauer's bias is because of his Everest bid. You are correct in stating that he likely has some bias in the story, but it more likely because of some childhood similarities. Evidence for this comes from quotes where Krakauer states parts of Chris's story "struck a personal note" for Krakauer. He even went so far as to write a bit of his own life.
As for the most important chapters, that is going to differ from reader to reader. But as you indicated chapter 1 is important because it introduces the reader to Chris. It shows him as an intelligent and thoughtful man/character, but it also shows Chris as woefully unprepared to live in the wilds of Alaska. The rifle is too small, boots aren't water proof, not enough food, etc.
I think 11 and 12 are important because they explore Chris's home life and gradually distance from his parents, especially after he found out that his father had fathered another child with Marcia. These chapters also show that Chris's decision to go to Alaska is not his first decision of this type.