Equip a car with an auto start device (currently available) that starts the car when the battery voltage drops to a pre-defined level, coupled with an inverter, a low RPM/High output alternator, and a decent sized deep cycle battery.
If the power fails, plug a cord into the inverter inside the car.
When the inverter has depleted the battery to a certain level, the car will auto start (outside by the way, not in the garage) and recharge the battery.
Assuming the load on the battery is 20 amperes per hour or less (approximately 200 watts), the engine would have a minimal run time to recoup the lost amperage from the deep cycle battery. With a full tank of gas, the car could provide power for quite some time. Additionally, the auto start devices on the market will kill the engine if someone attempts to drive it away without permission.
A larger inverter would draw more amperage and thus cycle the engine more often. However, with sufficent surge amperage ratings, a higher wattage inverter could run a fridge.