In all seriousness, the worst thing about an extended power outage is how much will it cost me to replace the contents of my freezer, the refrigerator not so much.
That is what we used for the other 3 walls, but the tub walls being tile directly on the cinder block (now illegal to build with), we were afraid we would break the wall, which would not only affect us but also our neighbor, being a row house. It was easier to build out the area above the tile with wall board and install a shower surround.
In all seriousness, the worst thing about an extended power outage is how much will it cost me to replace the contents of my freezer, the refrigerator not so much.