Maybe after we develop enough AI and robots to replace the billions of humans worth of labor that is done everyday.. Otherwise in a few months you'll be figuring out what you take for granted real fast. Anyone who has tried to repair a rusty car will understand that without fresh parts life is not going to be easy. Problem is we live in a world where nothing lasts forever so the idea of just surviving on what's left behind is not really sustainable in the way most people think. You would probably spend most of your days just breaking down materials.