Its not really post nuclear apocalypse, but I highly recommend I Am Legend by Richard Matheson. Its more about a viral apocalypse than a nuclear one, I admit. But its still about one man fighting alone in a world that has changed beyond all recognition, so there are some similiarities.
Also, don't be put off by the Will Smith film, the book is great and completely different from the film, which distorts the story completely. The book is also really short, you could easily read it in an evening. :read: