Final answer:
Jon Krakauer felt most guilty about the death of Chris McCandless, as he related to McCandless's adventurous spirit and reflected on his own experiences in 'Into the Wild'.
Step-by-step explanation:
The death that Jon Krakauer felt most guilty about was a) Chris McCandless's death. Krakauer related deeply to McCandless's adventurous spirit and empathized with his yearning for a life beyond the conventional path. In Into the Wild, Krakauer recounts McCandless's journey into the Alaskan wilderness and reflects on his own similar experiences, acknowledging a personal connection and a sense of responsibility, which contributed to his feelings of guilt over McCandless's tragic end.