I've also done the hand warmer trick during a winter power outage (you just have to make sure you have a supply at the house). When I lived in Vegas and there was a power outage in the summer, I filled 2 liter bottles with cool water, wrapped in towel and put in the cages so the snakes could cool off. Luckily in a big city power outages are usually not more than a few hours. Once we move to a more rural area, we'll also be looking into one of those small portable generators.