We've fortunately not had to rely on a backup generator in our lifetime, but with California's earthquake history we now our neighborhood's abundance of Prius vehicles could possibly be tapped for back up power according to this story (though with a lot of research)...
Electrical engineer John Sweeney used his Toyota Prius, an inverter which converted his car's DC power to AC for home use, with five gallons of gasoline to provide power for 3 days for his refrigerator, television, wood stove fan and several lights in his home during a long power outage caused by an ice storm that hit December 12th.
Here are some tips from Sweeney if you wanted to follow his footsteps:
1. Do not use an inverter larger than 1,000 watts because this can overload and damage the Prius 12-volt system. Keep in mind that running the inverter close to the 1,000-watt limit could also overload it because the startup power to many appliances greatly exceeds the steady-state power.
2. Follow normal safety procedures when dealing with the Prius 12-volt system. You should feel completely comfortable changing the 12-volt battery in the Prius by yourself before you attempt to make any changes to that system.
3. The Prius is a super low-emissions vehicle with a very efficient catalytic converter. In contrast, a standalone generator lacks a catalytic converter. Although the Prius is less risky than a standalone generator, the exhaust should be routed outside to eliminate the possibility of carbon monoxide poisoning. carbon monoxide is extremely dangerous and has no odor.
More details with insight from John himself over at The Harvard Press