A diesel generator would be nice, but we got a gasoline generator from Sears during a power outage in '06. The thing ran for a full week and burned a bunch of gasoline, but it got the job done. I think it was 3600W continuous, but I would have to look to be sure.

How much you need depends on you. We turned most of the circuits off to ensure that we wouldn't overload the generator, and had to manage the power to run heavy consumers like the coffee maker (e.g., unplug the refrigerator until the coffee was made).