A good book
A good book is great for two reasons: 1) it helps you make the most of your time during time-wasting activities like sitting on the subway or waiting in line somewhere and 2) it’s a signal to others that you want to be left alone. See a creepy guy eyeing you on the subway? Pick up your book. Someone getting too chatty on the bus? Pick up your book. It’s the universal signal for, “I’m not open for conversation.” And what woman doesn’t need that?