Earth Abides by George R Stewart is possibly the ultimate post apocalyptic book.
Written in 1949, it won a Nebula in 1951 and has been listed as the best science fiction novel of all time.
"Earth Abides begins in the United States during the 1940s, set largely in the Berkeley, California area, within sight of the San Francisco – Oakland Bay Bridge. Most of the Earth's population has perished from a virulent airborne disease. Isherwood "Ish" Williams, who had been temporarily living in a solitary California mountain cabin, is one of the survivors of the pandemic. He emerges from his scientific studies in the mountains to find his entire world barren of people. Isherwood explores the empty world and then settles down with a handful of survivors to begin the process of restoring the human race and civilization."
If you want to buy the book from amazon, click here - Earth Abides (S.F. MASTERWORKS)