1) The Book of Five Rings by Miyamoto Musashi
Written nearly 400 years ago by a Japanese swordsman, this book teaches principles that can be incorporated into many of today's situations. I first heard about this book on Joe Rogan's podcast during his interview of Andy Stumpf. Even if you don't want to dive into the entirety of the book, I would recommend at least considering the nine principles at the end of "The Book Of Earth."
2) Extreme Ownership: How U.S. Navy SEALs Lead and Win by Jocko Willink and Leif Babin
This book is full of lessons I have applied to both my professional and personal life. Some of my favorites are to keep your world small (when faced with a difficult and complex situation, complete one task, and then move onto the next, etc...) and communicate in simple terms (keep a plan as simple and straight-forward as possible).
3) Never Split the Difference: Negotiating As If Your Life Depended On It by Christopher Voss and Tahl Raz
I like this book because it is true-- there is more than one way to reach a deal without having to split the difference. I enjoyed reading the author's real life examples from his career as a hostage negotiator and my big takeaway was to make the other side feel like they scored a win, even if they didn't.
4) The Godfather 2 by Mario Puzo
The book. Not the movie. Although fictionally the book is written about our favorite Don, Michael Corleone, the story line is actually a fairly accurate account of the life of Salvatore Giuliano, Sicily's most famous bandit. Although it is a fascinating story altogether, a key takeaway is how honesty and integrity can transcend social oppression.