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Whenever Mark boots up a computer (ie. when finding the MAV) a sequence of source code is seen appearing on a screen. The code is written in PVS (Prototype Verification System), an experimental macro language which NASA actually uses and it's very plausible to appear on a future spacecraft. This particular chunk of code is from the already existing NASA PVS Library, and you can find that very piece of code as open source if you type a part of it into Google.
Rich Purnell slips and falls after he finds a way to rescue Mark Watney and tells his boss "I need more coffee." Donald Glover revealed in an interview that he slipped for real and just got up and continued to act, and the footage was retained in the final edits for the movie.
A real potato farm was installed on the studio lot with potatoes in all stages of growth so they could be used for filming.
NASA was consulted in order to get aspects of space and space travel, specifically in relation to Mars, with the most accuracy. NASA is federally funded, yet charges no one, including private for-profit organizations, any fees for use of and access to its archives and consultancy.
Sir Ridley Scott claimed that Matt Damon's solo scenes were shot for five weeks straight, after which Damon was relieved from the schedule. Consequently, Damon did not see most of his co-stars again until the cast was reunited to promote the film.
In the beginning, it is mentioned that a compromised space suit would cause decompression, giving someone about a minute to live. This is scientifically correct; contrary to popular belief, acute decompression in space or a planet with very low pressure like Mars does not cause the body to immediately explode or expand. Major effects include confusion, loss of consciousness and some subdermal bleeding, but it is generally agreed that a healthy human body can survive one minute in vacuum without life-threatening consequences.