The role of Ally was difficult to cast, and it took quite some time to find Emilie de Ravin. The main problem with de Ravin was the difference between her height (5 ft 2) and Robert Pattinson's (6 ft 1).
During breaks while doing a street scene, Robert Pattinson was injured as he was running away from a zealous fan and the paparazzi. He was not watching where he was going and ran into a parked cab. His injuries were not major nor life-threatening, but bodyguards still came to his rescue.
There is an easter egg in a conversation between two cops. One of the cops mentions the time 8:15, the number of the flight of Emilie de Ravin's character, Claire Littleton, on the TV show Lost (2004-2010).
Robert Pattinsons character orders a Tikka Masala in the restaurant. This is most likely a reference to him being a British actor, and that the Tikka Masala was invented for the British market and is virtually spice free.
The trivia items below may give away important plot points.
While sitting on the stoop of him mother's house, Tyler swears to Ally the cigarette he's smoking is his last one ever. This is possibly foreshadowing Tyler's untimely demise that occurs at the end of the film.