The first thing that you need to do is to determine your load - this is the amount of electricity you need to run your appliances. This will typically be measured in Watts. You can get this by, either measuring your specific appliances (or look for a label - most labels are in Amps; to get watts from that, mulitply by your household voltage - 110 V,) or you can do a Google search for "typical wattage for refrigerator."
The first (non-sponsered) hit I got was from Michael Bluejay - from his website, he seems to know his stuff. When you do a Google search, make sure that you get several different estimates, from several different sources, then take an average. If your appliance is older, you may want to add a small amount to the average (from 10-50% depending on how old, and beat-up, the appliance is.)
Repeat this for each appliance and then add all of the power ratings (the wattages) together. This will give you the MAX wattage that you need (unfortunately, heavier appliances like motors and heating elements have a startup wattage, which may be 50% above the usage rating - this only lasts for a few seconds though. Most generators will have both a normal, or steady, rating along with a "surge" rating to handle those startup wattages.)
Once you have these, you can select your generator, based on its power output rating. Be aware, however, that you will not be using all of these appliance at the same time. Even the "always on" appliances, like the refrigerator and freezer, only run for a short time, and then rest - depending on the temperature of the room, and the temperature setting. This can let you shave down the rating of the generator a bit.
