Continuity mistake: When the terrorists attack the van at the bridge, shortly after the explosion, you see the terrorists crossing the water in a boat. In the background you can see the van on the bridge with its doors open, shortly after this the terrorists are at the van doors demanding that the police open the van doors!
Continuity mistake: In the final fight scene with Harrison Ford, the bad guy's hair grows longer then shorter then longer from shot to shot.
Continuity mistake: When the bookshop keeper runs from his store in Piccadilly he enters Aldwych tube station this is impossible as said tube station is a 20 minute bus ride away. Also when he gets on the train the conductor announces that the train will stop at Leicester Square, Piccadilly circus (were he just left from), and Oxford Circus This is impossible, as no train on the London underground makes stops at all those stations. He would have to change trains at Piccadilly circus.
Continuity mistake: When Jack rushes to save his wife and daughter from the terrorists on the freeway, there is a shot where he turns onto another road. Throughout this scene his seat belt goes from being buckled, to unbuckled quite a few times.
Continuity mistake: When Cathy Ryan enters the highway off Rowe Blvd (before the crash), she's supposedly heading toward DC. In fact, she continues back toward Annapolis instead of toward DC.
Continuity mistake: When Jack Ryan gets in his car outside the Naval Academy to chase after the terrorists, he locks the driver's door as an officer comes up to the window to ask if he's okay. Moments later as Ryan is driving, the door is unlocked again.
Continuity mistake: When Sean Miller is being transported from the court, we see identical prison vans surrounded by Vauxhall Cavaliers. When the terrorists spring Sean from the prison van, the burnt out wrecks in front and behind the prison van are actually Rovers.
Continuity mistake: During the final boat chase, a fire is shown spreading in Ryan's boat around a green fuel tank labeled "100 Octane - low lead only." Seconds later, we see Miller shooting at a bright red tank labelled "Unleaded fuel only." 100LL is aviation fuel. Apart from that, the boat need only be carrying leaded or unleaded fuel - there's no reason for it to have tanks for both.
Continuity mistake: When Cathy Ryan is lying in the hospital bed, Jack gently strokes her forehead. The shot changes view, and Cathy's long hair is now in a different position around her neck and shoulders.
Continuity mistake: When Annette goes upstairs to the bedroom, we see a brief shot of her Uzi. There is no magazine inserted. Even the 10 round magazines stick out about half an inch and would be visible. When Jack picks up the Uzi after Annette is knocked out, suddenly, there's a magazine in it. (01:39:35 - 01:40:03)
Continuity mistake: When the three IRA members go to Kevin's house, he shoots one through the glass in the door. When he is leaving the house a short time later, the broken glass has a different shape. (00:18:15)
Continuity mistake: After Cathy Ryan's car's back window is shot out, she swerves to the right toward a black Jeep with license plate 934-072, but the angle changes and when the car hits the Jeep its plate is THA-1L3. (00:50:30)
Continuity mistake: Near the beginning, a woman goes into an antique bookshop and hands the man who works there a battered book. At first, the book is the right way up, but when he puts it down it's suddenly upside down. When we see the book again, now it's the right way up.
Answer: The movie never clearly says. It was some event that required tickets, as the mom runs back into the house to get them. And it was something Sally really wanted to go to, but it is never clear what the event was.