Your interviewers are not only interested in knowing if you exercise your mind, but they're curious about what kind of reading material you prefer and why. They're primarily interested in discerning what your choices say about you. Make sure the materials you offer are of a collegiate reading level or higher since they're looking for insights into your personality, emotional maturity, professionalism, and intellectualism. If you're reading multiple things simultaneously, don't hold that back. However, if you're not currently reading anything because you've been devoting your attention to other priorities, there's nothing wrong with admitting that. Share what you've recently read and what you're looking forward to reading next.