That would have to be.... The Bible.

It's more full of wisdom and truth than any other book I've ever read. There's not even a close second IMO

Desert Solitaire by Edward Abbey. I only discovered it fairly recently and it has already become my go-to read whenever I'm looking for some peace and simple natural spirituality with a generous side of denouncing the absurdity of modern culture and overaggressive "progress" and development.

How to Stop Worrying and Start Living

from Dale Carnegie. It's cheers up on bad days and gives helpful tipps and story (to think about it) for the live.

The Subtle Art of Not Giving a F*ck by Mark Manson

The German Grundgesetz if that makes any sense.

I try to find guidance on how to interact with the system, and how to interpret others actions from a very neutral but very comprehensive, guide to practical morality which is the GG for me.

Also I just love Art1 " Die würde des Menschen ist unantastbar"

Obviously it has some flaws, but if you interpret it enough it gives a good baseline for interpersonal stuff. Also it is the base law in Germany so practical value can also exist.

A Course in Miracles

@jack considering I never really read the bible and understood it completely, I'd say the one in the pic. Bought it in English when no course was held in English and no requirements were needed on getting anything of Informatics in English. I shipped this boy on literally the seven seas when changing continent. There are things I still don't understand such as Linear Programming ... and I will never read that section probably

The 7 Habits of Highly Effective People, Stephen Covey

Shakespeare's complete work folio.

The Fountainhead by Ayn Rand. It's terrible and fascinating at the same time. What I took away from it is that there is an inherent value in things you build yourself and a moral right to own your creations. I know the book is flawed in many ways, but I still think it's an interesting read. Wouldn't exactly call it my bible, but I don't think any book fits that description.