When you are planning your summer work, be sure to travel lightly. This means that you only take with you those items you are actually planning to work on. You don’t travel to the coffee shop with large tomes that you never get around to reading. You don’t overload your "to-do" list with items that aren’t absolutely necessary to get the dissertation done. Similarly, you don’t take tons and tons of books on your vacations. When you are working, work. When you are vacationing, vacation. Keep the dissertation from bleeding over into your play time.