Talk of The World, The Flesh, and The Devil reminds me that there is a kind of sub-genre of the post-apocolyptic film in which the known world is reduced to just two men and one woman.
Besides TWTFTD there is The Last Woman on Earth, an ultracheap production filmed, I believe, in Puerto Rico. One of the actors was Robert Towne, who later won great acclaim as the scriptwriter of Chinatown and other respected films.
Possibly the best such film is an eerie movie from New Zealand in the 80s called The Silent Earth. Like TWTFTD it also brought in racial overtones, as the remaining people are a white man, a white woman and a Maori man. In this story people who were at the point of death at a particular moment one morning are the only people remaining in the world; either everybody else vanished, or a parallel world was created where everything inanimate was duplicated and the people who were dying were transported.
Another sub-genre would be all of the zombie-type films such as Night of the Living Dead. While this picture is the one which “made” the class of film here in America, it in turn owed something to The Last Man on Earth, a cheap Italian picture with Vincent Price. Like the later film The Omega Man, it was based on a Richard Matheson novel, I Am Legend.
Finally, there are those movies which play the end of the world for laughs. Peter Cook and Dudley Moore appeared in a dark British comedy in the late 1960s called The Bed-Sitting Room about life in England after a nuclear war. I don’t remember much of it except that there was a part about how the government has to find out who is next in line to the throne and decides on an obscure working class housewife somewhere.
There is also The Night of the Comet, in which most of mankind is reduced to dust one night and the task of preserving civilization pretty much falls on a couple of Valley Girls with assual rifles. It is actually pretty entertaining.