You can legally store 250-1000 gallons of heating oil, which is diesel without the engine anti-wear additives. In most places you require a variance to store large quantities of gasoline.

Diesel does not go bad as fast as gasoline. I don't know if it goes bad at all. I know of people that have reclaimed heating oil from abandoned tanks after years of sitting and used it to power their equipment.

The trifecta would be oil heat & hot water, diesel generator and diesel vehicle. Fuel is interchangeable, though you can get fined for using untaxed heating oil for on-highway vehicle use. Apparently the die used in untaxed fuels will permanently stain the fuel filter, so even after you switch back you are still potentially at risk.

Smaller diesel generators can often be found at RV salvage yards. Onan is the brand name.

In NJ diesel has lasted longer than gasoline and is not subject to odd/even rationing. But when stations run out of gas they are closing down even if they still have diesel, and you still have to wait in line. Things might be different at truck stops. But even under normal situations, stations that pump diesel are few and far between. Of course if you are driving a diesel vehicle you will probably have that figured out.

Propane is a mixed bag in my state. It is an unregulated fuel so retailers charge whatever the market will bear. I the major regional LP supplier charges $18 to refill a 20# tank, but if you are a home delivery customer they only charge $9. I don't know if the lower price was a special or normal pricing, I don't have home delivery. Most retailers have gone to tank exchange only, costing an average of $20 for a swap.

Natural gas is the most affordable. Comments elsewhere about susceptibility to interruption during a power failure are noted, but I've never seen it happen. If I had natural gas available in my neighborhood it would be my #1 choice for cooking, heating and backup power. But I would still also maintain a supply of LP for emergencies, along with LP gas jets and knowledge of how to install/adjust them just in case.