CNN has an interesting article about several recent movies involving solitary characters. Examples are The Martian, Cast Away, Gravity, 127 Hours, All is Lost, Life of Pi, Wild, Locke, Buried, Moon, and Wall-E.
Movies featuring solitary characters present a film-making challenge. Typically character is revealed and the story is moved forward via the protagonist’s interactions with other characters. Went there aren’t any other characters to interact with, the writer needs to come up with innovative alternatives.
Based on the examples, the most common techniques are to have the protagonist keep a journal (expressed onscreen via voiceover), give them imaginary/inanimate friends, or give them a means to communicate with others even if it’s not in person.
It’s a short article, and I wish it was longer so it could have more in-depth analysis. But it’s definitely worth the read.
Warning: The article has a huge spoiler for Gravity. For the rest of the movies discussed, there are no spoilers beyond what you would have seen in the previews.