Other mistake: When in court as Harrison Ford is leaving after his testimony, Sean Bean puts his right hand behind his back a couple of seconds before the "officer" grabs it. (00:24:27)
Other mistake: When Sean and the two surviving terrorists are on the cliff, looking down at the two boats below, Sean fires a burst at the boats but there are no splashes anywhere to be seen.
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.