Life-changing books usually takes more concentration and are longer reads than most books, because you have to take the time to soak in the words to really remember them. Long flights are perfect for those types of books because you have very little distractions and all the time in the world to read a book of your choosing. Skip the quick romance novels or cheap thrillers for a book that will improve your life.
You can choose to read them through the old fashioned paperback medium or on a convenient e-reader. You'll be allowed to use the e-reader in flight but won't be able to access it when the plane is taking off and when it's landing.