First, always keep your phones and laptop batteries charged.
These should be readily available:
- Car Charger - to charge your phone via your car battery.
- USB Cord - you can plug your phone or tablet into your laptop (save power by not using the juice hungry laptop).
- Close down all Apps including WiFi and Bluetooth.
- Turn down screen's brightness.
- Note texting uses less power than a call.
Source: 5 ways to keep your phone charged in a power outage - CNN.com: