An extra phone battery
You can expect to use your phone’s maps app (and plenty of battery power) nonstop on your first visit to the city. This slim external battery holds more than two additional charges for any smartphone and comes equipped with two USB ports for easy simultaneous charging. And since it’s only a half-inch thick, it’s easy to slip into your purse or bag.
Mophie Powerstation External Battery for Universal Smartphones and Tablets, $46.43 on amazon.com