I think very little is worth it for three days every few years. Instead, I see the benefit of batteries + solar or a serious generator as reducing tail risk from rare serious disasters that leave the grid down for months or longer. These are not likely, but if they happen I'd want to have something in place.
I figured refrigerator uses about 1KWh per day. Just 2 days would require 200Ah of 12V batteries. Lithium looks attractive for weight and other factors but is more expensive than lead acid.
Have a large overhang that could temporarily be used to lay panels on too.
For portable AC unit, seems like would need another 10KWh per day or so of capacity. At that point, generator becomes more financially practical…
Also wrestle with how much I can depend on solar.
If only 100KWh of battery capacity was practical…