I bought an 80W panel on amazon for a little over $100. Just toss that on the roof of your car or canopy and use the included jumper cable -style clips to charge the car battery. A car battery holds about 300 watt hours - enough to charge about 20 phones. One of these panels can charge a car battery from flat to full in a few hours. We even lent it to our neighbors for about half an hour when they couldn't start their car because of a flat battery, and it worked like a charm.
Then just charge everything up using those cigarette lighter-usb port adapters, or the USB ports built in to your car if it has them. Or you could buy an inverter to get regular 120V household power out of it.