Post-apocalyptic story about the last person on earth

I feel like this has probably been written about plenty of times, but I can't think of one, and I suddenly have a hankering for the concept. I'm looking for a novel or novella about the last surviving person in the world after any kind of cataclysmic event. Very specifically the last (or functionally the last) person – that is, they don't encounter or speak to any other living person throughout the story. Anyone have any recs?