The Personal MBA. It's a book that covers several business concepts such as unique selling proposition, pricing models, permission marketing, return on investment, and other topics that can easily be applied toward one's personal life. I read this in high school or early college and it continues to shape the way I make decisions in my life. It is useful for people even if they are not running their own business. It has an online glossary as well, so you don't even need to read the book.
The Lean Startup. I read this during college or after college. It's about how market research is hard to do from a distance. Focus groups are a thing of the past. Consider your business as an experiment. You have to get started in order to start collecting data. Once you have a first customer and a product out in the open, this allows you to iterate rapidly to develop something that fits the market as closely as possible. The previous model of research, develop, and launch is archaic because it waits until the last step to perform market validation.
The Biography of Elon Musk. I read this in high school or early college. I don't worship Elon Musk, but it's interesting to demystify his empire-building. You won't learn very much from the book on its own, but it's an excellent book to understand different business concepts in play. The crux of his origin story is that he build something boring, but useful that was acquired, leaving him a small fortune. I would argue that's when his notable career began because he was guided by vision and he immediately used his small fortune to launch hare-brained ideas that were not necessarily going to be financially viable. His multiple businesses each help each other. While Elon Musk and I don't have identical visions, if you read the book to understand how people implement their vision in reality, this can be a useful read.
Paul Graham Essays. Paul Graham has some relatively high-yield essays on his website. He talks about default alive versus default dead, burn rate, and other business concepts.
Hacker News. The users on Hacker News trend toward insightful and you have a lot of founders on there who offer their perspective for free. You can start to understand how people think about issues. There's some pettiness on there, so you have to filter that out.