20. Printed copies
In my experiences I have found that using the old school method of having actual physical copies of all my reservations in my luggage and carryon gives me an added sense of security. Therefore, I always print out (or write out) all confirmation numbers, restaurant and event reservations, hotel room information, flights, and all other documented proof for the specific things I plan on doing during my trip. Additionally, I never go to Disney World without a working game plan and tentative itinerary. So I am always sure to make copies of these notes as well, and I always see that anyone else traveling in my party also has a copy.