It would not be a bad idea to pick up a portable battery charger for your cell phone. They can be bought at walmart's best buy and other places. If fully charged you can charge a cell phone or tablet 3 or more times depending on what size charger you get. Just make sure to charge the charger before the power goes out.
For informational purposes:
30 Best Portable Battery Chargers | Android, iPhone, or iPad | Digital Trends