I bet there will be people on the street who will ring up your sale, without a cash register if you have legal tender or gold. There probably won't be any 'clerks' in the stores anyway, and all the good stuff will already have disappeared.
Best not to let those people know you have any kind of money.
Of course out here in reality we know those kind of black outs are pretty rare. Longest power outage I’ve lived through was about 11 hours. And I only had to drive about a mile and half to be out of it. This summer we had a nasty storm, friends of mine live in a neighborhood that took 4 or 5 days to get power restored. They stayed in hotel 2 or 3 miles away. So power outage is really just a thought experiment.