The trailer shows an alternate version of the club scene kiss with Nick and Norah. When Tris comes up to ask them how they met - it is Nick who tells Tris that they have the same dentist. In the actual movie, Norah is the one that tells this to Tris.
Norah is a Jewish girl attending a Catholic high school. This is explained in the book that Norah wants to attend any school Caroline does, but due to Caroline's obnoxious behavior, she's kicked out of every school she's been to and is only accepted at a Catholic school.
When the Queercore band members arrive at Nick's house they knock the trash cans over and a Tide detergent container spills out on the lawn. A scene later when they show the spilled trash there is a milk container next to the Tide container that was not there before.
When the convenience store owner is talking to Nora about having to chip the barf out of the ice cream cooler again, Tris pushes open the door and walk into the store, dropping her arm to her side. In the next shot, Tris is again seen with her hand on the door and again stepping into the store.