Date Night

Phil and Claire Foster (Steve Carell and Tina Fey) are a married couple from New Jersey with two children and whose domestic life has become boring and routine. Phil is a tax lawyer while Claire is a realtor. They are motivated to reignite their romance after learning that their best friends, Brad and Haley (Mark Ruffalo and Kristen Wiig), are planning to divorce to escape the married-life routine and to have more excitement in their lives.
To avoid the routine that had become their weekly "date night", Phil decides that he will take Claire to a trendy Manhattan restaurant, but they cannot get a table. Phil takes a reservation from a no-show couple, the Tripplehorns, despite Claire's misgivings. While eating they are approached by two men, Collins (Common) and Armstrong (Jimmi Simpson), who question them about a flash drive they believe Phil and Claire stole from mobster boss Joe Miletto (Ray Liotta). Phil and Claire explain that they are not the Tripplehorns, but the men threaten them at gunpoint. Not seeing any other way out, Phil tells them it is in a boathouse in Central Park.
At the boathouse, Claire pretends to search; while Collins and Armstrong's backs are turned, Phil hits them with a paddle and escapes with Claire on a boat. At a police station, Phil and Claire talk with Detective Arroyo (Taraji P. Henson), but discover Collins and Armstrong are also detectives, presumably on Miletto's payroll. Realizing they cannot trust the police, they decide to find the real Tripplehorns. They return to the restaurant and find the cellphone number of the Tripplehorns.
Claire remembers a former client, Holbrooke Grant (Mark Wahlberg), is a security expert and James Bond-like action hero. He is consistently seen never wearing a shirt. At his apartment, Grant traces the cellphone signal to an apartment owned by Tom Felton. Collins and Armstrong arrive, but Phil and Claire escape in Grant's Audi R8.
They arrive at Felton's apartment and break in. They question Felton, nicknamed "Taste" (James Franco), and his wife "Whippit" (Mila Kunis) about the flash drive and Joe Miletto. It turns out that they went to the restaurant, but left when they spotted Collins. Realizing they are in danger, the couple give the flash drive to Phil and flee. When Phil and Claire get back in the Audi, Armstrong and Collins shoot at them. Phil and Claire crash the Audi head-on into a Ford Crown Victoria taxicab, resulting in their Audi and the Ford being attached at the bumpers. Phil and the cab driver (J. B. Smoove) decide to drive off to get away. Phil climbs into the Ford to navigate while Claire navigates the Audi. Phil checks the flash drive on the driver's Amazon Kindle and finds pictures of district attorney Frank Crenshaw (William Fichtner) with prostitutes (early in the film, a press conference shows Crenshaw highlighting his integrity platform). After evading Collins and Armstrong, they are eventually hit and are separated by an SUV. The cab falls into the river; Phil and the driver escape, but without the flash drive.
In a subway, Phil determines that Felton obtained the flash drive to blackmail Crenshaw. They return to Grant's apartment, and Grant is reluctant to help after becoming exhausted by their incompetence, but Phil begs and he agrees. Phil and Claire go to an illegal strip club that Crenshaw frequents, with Claire under the guise of a new prostitute and Phil as her pimp. After doing a pole dance for Crenshaw, they confront him and tell him they are the Tripplehorns. Collins and Armstrong come in and hold them at gunpoint and take them up to the roof with Crenshaw. Miletto arrives with henchmen and it is revealed that Crenshaw has been paid by Miletto to keep him out of jail. When Phil mentions the photos, a feud escalates between the mobsters and Crenshaw, Collins and Armstrong. Phil asks Claire to count to three (her typical method of calming their children). When she does, a helicopter appears and Arroyo and the SWAT team come onto the roof to arrest Miletto, Crenshaw, and everyone else. It is revealed that Phil was wearing a wire courtesy of Grant, who informed Arroyo of the situation.
After being declared heroes, Phil and Claire enjoy breakfast at a diner, where Phil admits he would marry Claire and have their kids all over again if given the chance. When they return home, they make out on the front lawn.

Question: What do Collins and Armstrong think Phil and Claire stole?
Answer: A flash drive