What do we learn about McCandless’ childhood and its foreshadowing of his future?

Even in high school McCandless is caught up in serious questions, becoming obsessed with fighting racial oppression in South Africa, and spending weekends in the seedier neighborhoods of Washington, D.C., talking to prostitutes and homeless people, buying them food and giving them earnest advice on how they can improve their lives. One time he even brings a homeless person home with him and secretly sets him up in the trailer his parents have beside their house. This foreshadows his concern for things other than material posessions, social stature, or money.