Like books or movies? There's Stephen King's "The Stand", "Metro 2033" (I haven't read the book, but the videogame is fun), The "S.T.A.L.K.E.R" videogames (loosely based on the movie of the same name) and of course Mad Max.
If you're looking for material, I often base my stuff off of Metro 2033, the S.T.A.L.K.E.R., Fallout and Last of Us video games, as well as TV and film like the Walking Dead, Planet of the Apes, 28 Days Later etc
Well, all these video games are based on real fiction. Metro 2033 is post-apo in Moscow tube-stations. Stalker is based on also a Russian sci-fi literature "Roadside picnic". The Road is also good book, that got movie done. There is also the classic "Lords of the Flies" which is touching upon social side of things. But what would be a definite post-apo literature in sci-fi, that would be interesting to know.
I also often base the events of my campaign of off classic literature or actual historic events- the players unknowingly had a role in what was essentially Hamlet in the Ark, and the events played out similarly to how they did in the play- except instead of a duel with Laertes using poisoned swords, they shot each other.