Double dipping is considered a bad thing when it comes to food. It's not polite to put the same piece of food back in the communal dip. But when it comes to reading, double dipping is a great thing. If you know you will have to spend time waiting, or even if you think you might, a book will make the time go faster. Books are portable, and can be enjoyed almost anywhere.
I like to take nonfiction with me when I think I will be reading on the go. It seems easier to read in snippets when it is nonfiction. Fiction can be more difficult to wrench myself away from.
Typically, everywhere I go, a book goes. I choose my purses based on whether they are big enough for a standard book. I have read books in waiting rooms, fast food drive-thrus, parks, hospitals, and that is just the beginning. (I don't recommend reading and driving as a double dip. It's extremely hard and dangerous.)
What about you? Do you take books with you on the go?