The trick with a gas generator is to have an electrician install an interlock on your electric panel along with a hookup to your generator. Then it's a snap to switch over to the generator, and start it.

The only trouble is that gives no indication when the power comes back on. So there you are, generator blasting away, while power is restored. Leave a couple circuits always connected to the line power, and hook those to a radio or a light so you know when the line is back up.

P.S. if you get a generator with an electric starter, odds are good the battery will be dead. The trick is to add a couple power posts to it, so you can jump start it with your car.