Difficult to pick just one, but I will go with The Stainless Steel Rat. It was a great introduction to the idea that society's rules don't always make sense. I haven't read it since I was in grade school, so I don't know if anyone older would enjoy it. But it definitely planted the seeds of anarchism, hacking, punk, and not taking rules too seriously.

https://en.wikipedia.org/wiki/The_Stainless_Steel_Rat