This is both a film and a book. To avoid the cliche I will quickly say, the film is better than the book. It captures the environments through which the maverick/ selfish/idealistic/ wonderful/ tragic (delete as you wish) central character Chris McCandless travelled and ultimately perished quite beautifully.
McCandless, was a disillusioned high school graduate in the USA in the early 90s. On graduating he decided to sever all ties with his materialistic, American dream infected parents and follow the lead of his heroes Jack London, Henry David Thoreau, Leo Tolstoy and Doctor Zhivago.
The book gives more background as the author travels to meet some of the people who came across McCandless as he hitchhiked around North America. It won't spoil the ending if I tell you that McCandless came to a tragic and very unfortunate death in the wilds of Alaska (this is told at the start). A quote from a letter sent by McCandless to an old man he befriended sums up what the film and he was about:
So many people live within unhappy circumstances and yet will not take the initiative to change their situation because they are conditioned to a life of security, conformity, and conservatism, all of which may appear to give one peace of mind, but in reality nothing is more damaging to the adventurous spirit within a man than a secure future.
This story, whether read in a book or watched on film, is brilliant education for sustainability, it teaches us to look way beyond the normalising effects of 21st Century life and to imagine wonderfully different ways of living