The Lathe of Heaven by Ursula Le Guin First read during my high school years in the Amazing SF magazine; and was later published as a book. The work was criticized by the 'elite' of the SF community at the time. Have recently re-read and got the same impressions of how as both a species and as individuals we are fools that understand very little; that is, we are too stupid to know that we are stupid.
Calvin and Hobbs by Bill Waterson. Was my favorite non-mandatory read during my college years. Calvin Ball can teach us much about life, and his snow-men art is the dark that we always be in all of humans.
Marine Corps Reference Publication (MCRP) 3 Rifle Marksmanship. [this is the current version, but am not certain of the designation for this manual when I first read it during the late 1970s]. This summarized the philosophy of combat, the physics of interior and exterior ballistics, and describes the zen-like state of the marksman. It is not as sterile as the US Army marksmanship manual, is more complete treatise of combat shooting and weapons care, and is brutally honest in that the USMC is preparing you to efficiently kill other humans. Very sobering.