For very early, very late or just very lazy classes, I have found it beneficial to start the hour off by an activity that gets the students up out of their seats and gets their blood flowing. I introduced two such activities last week.
The first was the culmination of the first day's ice breaker activity, where students had to interview each other and introduce their partners to the class. I took notes as they spoke and used the information for the next class in a "Who's Who in 106?" game: I made a worksheet with a question about each student (i.e. "Which student climbed Mt. Rainier this summer?"). The students then walked around the class matching each question to the appropriate student.
Yesterday, when reviewing the first chapter of BNCH, I used cardstock and magnetic tape to make strips of reader characteristics. Each student received one strip and had to approach the board and place their strip in one of two categories: "characteristics of effective readers" or "characteristics of ineffective readers." We then discussed each characteristic, rearranging the strips as necessary.
Well, these are just a few ideas that I've used to -- I hope -- make my class a little bit more dynamic and active.