You'll be out of the hotel all day, so you've got to take everything you'll need for the next 12 hours of sightseeing. What goes in your day bag? All the essentials--but not enough to weigh you down.
Choose a lightweight, comfortable bag or backpack with several pockets. Put the same items in the same pockets every time so you can grab your camera fast enough to get those great shots.
Carry your driver's license, passport, money, credit cards and travelers' checks in a zipper-lock plastic bag, and place in a closable inside compartment. Is your book a must-have? What about pen, notepad, camera, memory cards and cell phone?
Check the weather and add a hat, sweater, windbreaker, gloves, scarf or umbrella as necessary. Keep in mind that although fleece is bulky, it's light and will keep you warm even if you get caught in a sudden downpour.
Put one-day's medications in a small pillbox. Add lip protection, sunglasses, travel-size bottles of saline solution (if you wear contacts), sunscreen and a tissue pack. Zip it all up in one plastic bag and stash in an outside pocket for easy access.