You need look no further than the way that works by key transcendental thinkers such as Thoreau and Emerson are used in the book itself. For example, you will have noticed the way that each chapter begins with one or two quotes from varioius books. The quotation at the beginning of Chapter Six comes directly from Thoreau's Walden:
The true harvest of my daily life is somewhat as intangible and indescribable as the tints of morning or evening. It is a little star-dust caught, a segment of the rainbow which I have clutched.
This quote of course captures the importance of the return to nature philosophy that McCandless tried to embody in his life. During the book, various others who tried to similarly return to nature are mentioned, especially in Chapter Eight, where the fascination of Alaska's untrammelled wilderness is explored at length. Throughout the novel, transcendentalism is refered to in the author's attempt to explore what drove Chris McCandless to act as he did.