If you will be traveling by car, consider bringing a Car Charger Adaptor.  These adaptors will work in both US and European cars, plugging directly into the cigarette lighter or special outlets that most newer cars now have.  Having an adaptor will allow you to charge your devices while driving.  If you will be using your phone's GPS Navigation while driving to your next destination, you will find that your phone's battery will be drained at a much faster rate.  Keeping your phone plugged in while driving will help ensure your battery remains fully charged.

Car Charger, Sicodo 2-Pack 3.4A Dual USB Port Rapid Car Charger Adapter Charger your iPhone 7, 7 Plus, 6 Plus, 6S, iPad, Tablet, Samsung Galaxy S8, S7 edge, HTC, Sony and Other USB Devices Compatible with multi-species USB devices, Such as iPhone, iPad, Tablet, Samsung Galaxy, HTC, Sony, Blackberry, LG, Nokia, External portable battery, Digital camera, MP4, GPS and more USB devices Efficiency and Speedy Input: 12-24V Output: 5v / 3.4A Max 2 smart USB ports allowing you can charge up 2 mobile devices simultaneously at full speed while on the car Safety and Reliability: Intelligent circuit protections against overheating, over current, and overcharging Charging will stop automatically when battery is full to maximize the safety of your devices Unique design having blue LED indicator light lets you know the status of the charge and gives your car charger a special look! Sturdy and Durable, made of high quality fire proof material & anti-oxidation aluminum