Converting a freezer to a fridge by means of a different thermostat is an excellent idea as in the article linked to above.
Not however as original as the author believes, I did it years ago, and cant be the only person to have thought of this.

Although a great deal of energy is saved thus, remember that line voltage power is still required.
In any serious or long term emergency it is unlikely that grid power will be available. That means reliance on an inverter. If life depends on an inverter, then it should be duplicated.

Another option is a very high efficiency DC refrigerator, these are sold for off grid homes and use little power.
They work directly from a battery without an inverter. The battery may be charged from PV, a vehicle, or by limited generator running.

Or an absorption type where it uses a small flame. My camper fridge is like that and as long as the camper sits on the level garage floor it cools fine, doesn't work so well anywhere else but for a home fridge it would work as the flame is pretty small.

An absorbtion fridge when burning propane, or less commonly oil, has a lot to recomend it.
A continual supply of propane or other fuel is required, but the consumption is small and a large propane tank will work the fridge for months.
Although some absorbtion fridges can also be run on electricity, this can not be recomended except briefly in a moving vehicle when propane burning might be unsafe.
An RV type absorbtion fridge if electricly powered can use more KWH a day than a full sized domestic model.

My thought there was amybe somehting like a wood gassifier to provide a small amount of fuel to burn, is only a small flame like a pilot light.

for a backup....one of the commercial thermo electric 12v cooler chests with a cigarette plug or a DIY Peltier thermo electric module in a small styrofoam cooler could be run by a 12v battery with PV solar charger ...