What are examples of pathos in Into the Wild?

In using pathos, an author appeals to the emotions of the reader. To be convincing, a written work must use both pathos and logos. Logos is an appeal to logic: it persuades through use of facts, statistics, and other details. In Into the Wild, Krakauer effectively uses both pathos and logos, but here we will focus solely on pathos.
Krakauer primarily uses pathos to urge us to sympathize with McCandless. After Krakauer wrote the original article about Chris that led to his book, many readers were convinced Chris was foolish, impulsive, and possibly suicidal. In this book, Krakauer instead paints a much more positive picture of his subject as an idealist whose plans went awry.
One way Krakauer builds pathos is by showing how the young, handsome, and charismatic Chris befriended people who were older or perhaps a little odd. He touched lives by living in simplicity and reaching out to people who struck him as authentic. One such friendship was with the eighty-year-old Ron Franz, and Franz would later speak about how close he felt to Chris:

“Even when he was sleeping, I was happy just knowing he was there.” At one point Franz dared to make a special request of McCandless. “My mother was an only child,” he explains. “So was my father. And I was their only child. Now that my own boy’s dead, I’m the end of the line. When I’m gone, my family will be finished, gone forever. So I asked Alex if I could adopt him, if he would be my grandson.”

This request touches our hearts because it shows how deeply Franz felt affection for McCandless and speaks to the influence the young man had on the people he met. We feel good about McCandless because of this story.
Krakauer handles McCandless's death with pathos, showing how brave and happy Chris looked and acted even in his last days. As we can see, from the passage quoted at length below, the many details Krakauer includes touch our emotions and build our sympathy for him:

McCandless penned a brief adios: “I HAVE HAD A HAPPY LIFE AND THANK THE LORD. GOODBYE AND MAY GOD BLESS ALL!” Then he crawled into the sleeping bag his mother had sewn for him and slipped into unconsciousness. . . . One of his last acts was to take a picture of himself, standing near the bus under the high Alaska sky, one hand holding his final note toward the camera lens, the other raised in a brave, beatific farewell. His face is horribly emaciated, almost skeletal. But if he pitied himself in those last difficult hours— because he was so young, because he was alone, because his body had betrayed him and his will had let him down—it’s not apparent from the photograph. He is smiling in the picture, and there is no mistaking the look in his eyes: Chris McCandless was at peace, serene as a monk gone to God.