Write "terms to know" on the board and then have each student erase one and tell the class something about that term (definition, connection, example, etc. Can also use a graffiti board as an Activating Prior Knowledge lesson.
Make and put on the door - Teach-A-Roo: Ticket Out the Door! This can be used as an exit ticket. You could put critical thinking or math on the door. This gives the students something to do when waiting at the door.