You will need:
1. An old lawnmower.
2. An 12v auto alternator.
3. A car battery.
4. An inverter (12vdc = 120vac)
5. Wire, bolts, plugs, pulley, belt, other small stuff.

I bought a "battery isolator" and connected it to my jeep's alternator to
charge a second battery which powers a 3500 watt inverter. The isolator
prevents the main battery from draining so the car can be restarted. A car
can safely idle for hours to charge the battery and run the inverter, while
consuming little fuel.

When hurricane Isabel hit and power was out for over a week, I had plenty of
power to run the refrigerator for several hours a day (the ice never even
melted). I could run flourescent lights and my computer all day. Among the
advantages of this is it's MUCH quieter than a generator (silent when the
car isn't idling), lots easier to store and very portable.