Earthships come to mind when talking about recycled buildings. Made of upcycled or recycled materials.
https://www.earthshipglobal.com/
Old propane tanks can be turned into heaters, smokers and even grills as well as old water heaters. I know a welder who loves using old stainless steel tanks from water heaters and making grills and smokers out of them. Also washers and dryers have drums that are very usable for such things. I even have a buddy who turned an old fridge into a cold smoker for doing fish... I can see lots of ingenious uses for many modern conveniences that would not be functional in a PA world unless they had power and some repair maintenance knowledge..
Recycle would and could be very profitable to anyone willing to go into the cities and scrounge for stuff..