McCandless didn't bring those infamous books to the bus; Krakauer inferred that detail so he could presume more about Chris's character.  The previous year, current Fairbanks professor Dr. Jeff apple Benowitz brought the books with him for his planned month-long ascent of Mount Brooks (he didn't make it and spent a night in the bus on his return, ditching the extra weight of the books).

https://www.adn.com/books/article/fiction-jon-krakauers-wild/2015/01/10/

You can also find this information in the UAF library basement, in Jeff's book "Hitchhiking Up Mount McKinley".