I have a 5200 watt generator with a 5 gal tank.Check the label of any appliance. There will be a WATTS rating. The total watts rating of all equipment must be well below the total watts rating of the generator. Some devices have very high starting power requirements. Mostly those with motors. Once started, power requirements drop.
Most generators are rated at their peak load ability.. They can't run at that load very long. Be sure you check the constant duty load for your calculations.
We run the:
46" big screen/direct TV (note do not allow you big screen to go idle. hummidity will set up in it and will damage it if the power is out for more that 4-5 days!)
two lights at night.
toaster, can operner,microwave when needed.
all this last for 22 hours per 5 gal of gas.