Jenny's friends Hattie and Tina in An Education. They hang on every detail of her unfolding love story, but either they dump her or she dumps them about midway through the plot, and they're never seen again.
Tahei and Matashichi from Akira Kurosawa's The Hidden Fortress. R2-D2 and C-3PO are loosely based on them.
Hot Fuzz has Andy Cartwright and Andy Wainwright, referred to as "The Two Andies."
Hannah Montana: The Movie has Rico and Oliver as two regular school guys helping out at Lily's party and not having any importance to the plot. In the TV series, it's not quite like that as Oliver in particular does have some central roles.
Kafka has the two childishly stupid assistants, two twin brothers who keep fighting constantly and are cause of some of the best comically kafkaesque scenes of the film, like when they try to open the writing desk in Kafkas office or play around with the typewriters. It is later revealed that they have been Evil All Along.
A very early film example are "Charters and Caldicott" from The Lady Vanishes (and a half dozen other movies of the early 40s) who spend their on screen time mostly obsessed with the current cricket scores. They have their very own adventure in Charters and Caldicott by Stella Bingham. The pair are still obsessed by cricket and go from lunch at their club to Caldicott's flat to settle a point in dispute with his 'Wisden' a Cricket reference work. They discover the body of a young woman on Caldicott's bedroom floor. Her purse identifies her as the daughter of an old friend. But then another young woman appears claiming to be the * real* daughter and that her father has been murdered - then it starts getting complicated.
In The Life and Death of Peter Sellers, Spike Milligan and Harry Secombe (Peter Sellers' colleagues from The Goon Show) pop up in a largely non-speaking capacity several times after the opening scene of a show recording, symbolizing Peter's disconnect with his old friends and his first great success out of his ambition to become a film actor, and his eventual alienation of virtually everyone he was ever close to. (Peter was actually quite close to these two guys throughout his life, but it's the kind of movie that's not interested in the good times.)
"Manos" The Hands of Fate has those two teenagers who are sitting in a car making out with each other. They have no relevance to the plot in any way. It also has a pair of policemen, whose presence at least makes sense, even if they are just as meaningless.
Doctors Newt Geiszler and Hermann Gottlieb from Pacific Rim.
The Pirates of the Caribbean series has two sets of these. One set are pirates (Pintel and Ragetti) who explain the convoluted plot to each other, and the other, less-used pair are a duo of Laurel and Hardy-inspired redcoats who are always debating things (Murtogg and Mullroy). Both pairs end up on Barbossa's crew at the end of the third movie.
Mia's maids in the second The Princess Diaries movie. One of the few funny bits in the movie is when Lilly lampshades this by calling them Rosencrantz and Guildenstern. And then Lenny and Squiggy.
R2-D2 and C-3PO have been Those Two Droids for nearly 100 years, present for many turning points in the galaxy.
Later (non-canon)comics reveal that practically any pair of Stormtroopers, Imperial guards, Clone troopers, Sandtroopers, no-name jedi, etc., is likely to be Tag and Bink, a pair of screw-ups who fumble their way from the Jedi Academy to the Tantive IV to the Death Star (both times), etc. Literally, pretty much any time you see two anonymous stooges in the movies, that's them right there.
Val and Earl from Tremors manage to be this trope despite also being the unlikely heroes of the film.
The two hillbillies that are seen watching the practices and the games in The Waterboy.
The two brownies (no, they are little people, not chocolate) Franjeen and Rool in Willow.
The two NASA recruiters, one played by Jeff Goldblum. in The Right Stuff. Also apparently Gagarin and Titov in the intelligence film from Russia, which is lampshaded by the first pair, who argue which is which. The former pair accidentally put on each-other's coats, which don't fit, are apart only momentarily, and serve as the main comic relief in the first half before the movie becomes a more sober historical epic.