You can buy a new gasoline generator and leave it in the crate until you need it. When you uncrate it, check the oil and fill it with gasoline it will likely start and run. But the next time that it is needed the carburetor will be fouled from the gasoline residue and will have to be taken apart.
Diesel fuel is safer to transport and store but it gets thick at low temperature and gets jellied from a fungus that grows in the tank. Most Diesel fuel has a fungicide added.
Propane does not foul the carburetor but requires a 500 gallon tank to run a 20 KW generator (which will run a whole )house. The tank can be filled only by your contracted LPG supplier.
Natural gas is similar to propane but requires no tank. An earthquake may interrupt your supply but nat. gas is the least hassle most of the time.
Engines are made that will run on 2 or more fuels.
Thank you for the info. I did not think of natural gas.
I will research it.