You can do that so long as nobody else in the area affected by the outage had the same idea and got there before you.
The last major outage (due to an ice event), I hit the stores within the first hour of the outage and they were already cleaned out of water, propane, ice, and getting rapidly cleaned out of other supplies.
I really don't want to be rude here, but I live in a place where we constantly throw the frozen stuff outside into the snow when the power goes out, so I'm genuinely confused.
If it was an ice event, why would you have to travel to get ice?
I've lived in places where the "ice event" that caused the power to go out was freezing rain. That kind of ice can make trees heavy enough to lose limbs into power lines and makes roads slick enough for vehicles to crash into transformers and power poles (hence the power outages), without outdoor temperatures necessarily being cold enough to preserve frozen goods and without there being enough easily available ice outside (e.g. ~.5cm covering on all surfaces) to bring inside for stuffing the freezer.
That is almost exactly what happened here. We basically had sleet for about a full day, it was relentless. In an area that never snows and rarely freezes, a neighbor went actually ice skating down the street. I still have microspikes from my previous life in the mountains, and was one of few people who could get around confidently -- and even then, it was a bit sketchy here and there.
I've never seen anything like it. Individual blades of grass were embedded in solid capsules of ice. I regret not taking the time to get the camera out and do a bunch of photography, but I had my hands full the entire time.
A few nights later, the ice had barely begun to thaw, and then it refroze and then started snowing. I stood outside my home for a bit in the darkness, and listened to the sounds of tree limbs cracking, breaking, snapping, and crashing, like a steady rhythm, for a while. Just, "boom, crash. ... boom, crash. ... boom, crash. ..."
We're getting side-tracked a bit here. In this case: it happened in an area where most folks are accustomed to mild weather year-round and I don't recall seeing even a single box of food kept outside; I was out for propane, and only noted a few other things that got hard to find much more quickly than expected; the power outage itself lasted until long after the freezing conditions did, because the outage was caused by massive tree destruction that took out power infrastructure over a large area. This happened back in January and there are still cleanups happening here and there from it.
The bell curve for outages seemed to be a few days at the least, to about 5 to 10 days for most, to about three weeks for some in outlying areas. You can find some reasonable articles by searching for "2024 oregon ice storm".
In any case, point was, whatever supplies you think you'll need for an extended power outage are likely to become scarce really quickly.
The difference is the battery can engage automatically. Do you want to monitor for the rare, yet anticipatable event?
A self-critique: power outage isn't going to occur without notifying the person, except for maybe being out of town. That said, one less problem to solve in response to rare, anticipatable event.
Get a 12V power inverter and power it off and idling car, or even better an EV. The max draw for most fridges/freezers isn't very high actually, and the average load is very low.
You can 'run' a freezer for about 10-12 hours by purchasing 5-10$ worth of ice from a grocery store.
For something that happens twice in 25 years, that seems like the more pragmatic way to go?