In no particular order, and only a tiny sampling...
Rumi, as translated by Coleman Barks. There are a bunch of books to pick from. Barks makes poetic translations more so than literal, so some Rumi scholars don't like his versions but while the literal translations are closer to Rumi's actual words, Barks' translations seem to get closer to what Rumi was trying to articulate.
In the Absence of the Sacred: The Failure of Technology and the Survival of the Indian Nations
by Jerry Mander (yes, that's his real name)
Quantum Psychology by Robert Anton Wilson (everyone should have some Basic Training in guerrilla ontology IMO!) Link is to PDF download of actual book.
The Blind Watchmaker: Why the Evidence of Evolution Reveals a Universe without Design by Richard Dawkins. We might believe we know what the Theory of Evolution is all about, but it turns out most of us are wrong and that goes for whether we fully support it or think it's an evil conspiracy to lead people away from God (or something in between). I include it here because it's quite an eye-opening read, but more importantly if we like to contemplate or discuss Evolution in any context or debate it from any angle then it's helpful to understand exactly what it is that we're talking about.
This guy's essays: http://www.paulgraha.../articles.html Some are highly-technical and not really applicable unless one is heavy into coding and others are concerned with tech startups and funding them (and are fascinating for those who are interested), but this essay called "Why Nerds are Unpopular" is an example of his expository/philosophical writings, and a necessary read for any kid who reads the kinds of books recommended in this thread because they're probably "nerds," or would be if the term wasn't pretty much obsolete.
These are a few other essays I found especially insightful: Maker's Schedule, Manager's Schedule (THIS is why tinkerers and DIY-types, aka "makers," don't get along with management-types, or for that matter any arbitrary, inflexible bullshit like clocking-in and clocking-out. It's the most eloquent explanation I've read of a phenomenon that's infuriated and frustrated all mad scientists and their eternally-baffled managers at some point).
This one is sort of related to the above essay: You Weren't Meant to Have a Boss
A dose of humility is good every now and then: Why Smart People Have Bad Ideas
Fascinating perspective on the arbitrary social construct we call "morality:" What You Can't Say
I'd also suggest signing up for the RSS feed and reading... pretty much every single article published on this blog. It's a site dedicated to answering the question you posed with this thread, so it's like a portal to hundreds of incredible books, essays, and assorted writings that were "picked" specifically because they will stimulate the "brains" of people who actually use theirs, hence "Brain Pickings." Today's post seems particularly relevant to the topic at hand, interestingly enough.
Also, I'm glad to see the mention of Tom Brown, jr., As some of you know I've long been a dedicated student of all things Tracker and highly recommend his books, but more importantly to attend his actual school. And the younger someone starts, the better. I would go so far as to say that going to the Tracker School and living the teachings in the woods (to the extent I could) for a few years was among the most profoundly influential experiences of my life.
Nothing inspires self-confidence like -just as an example- knowing you can stop your car, jump out, and bail into the bushes at any random spot with nothing more than what you're wearing and be just fine (or if necessary, vanish into thin air and evade pursuit by human, dog, or helicopter-mounted thermal imager). Living in full-survival in wilderness also strips all of the bullshit off of our notions about reality because in that context, if our notions are wrong... we'll likely die.
Profound insights and philosophical musings found in books and such are all well and good, but IMO they are just the window-dressing of lived experience, aka "dirt time" in Tracker jargon. Like an ancient Wise Ass once said, "I hear and I forget, I see and I remember, I do and I understand" (I think it was Confucius, who was a smart dude but also kind of an asshole so I tend to avoid him).
Finding a healthy balance between reading books/absorbing abstract knowledge and "dirt time" seems to me like the way to go to maximize the benefits of both.
And of course, now matter how crazy life gets, never forget the wise words of a modern American sage who died way too young but probably had a fuller life than most who live twice as long (Bill Hicks): It's just a ride...