"How to win friends and influence people" by Dale Carnegie.
Amazing book, often recommended by Warren Buffet in various Interviews.
Really changes the way of how you interact with people in different situation.
Not wanting to say too much but it will improve both your business life and private life.
Has a bit of psychology, a bit of sociology, a bit of philosophy and a bit of solid practical advise in it.
Other than that... Just google for a list of good books about business and finance.
Having knowledge about money and finances in general is one of the most important things to have.
You can always read IM stuff at home...
On vacation I always try to read more complex and "deeper" books so I really have the time to understand, not just to read them.