Get off the podium. Turn on the met and walk around as they are playing, they aren't watching you anyways. You hear more that way too. Proximity is important when dealing with kids who are not following procedures.
Praise and reward the kids that are doing the right things. Praise the sections that are always on task. Turn it into a positive situation. Kids who take their instrument home occasionally get a new pencil with a note in their locker. Look for ways to promote the good things that are happening. It will also help you by focusing on that.
Allow for a LITTLE "personal time" in sectionals. A little more free talking, that's where we build the relationships that help us in the full rehearsals. If your sectionals are short, then before and after. Ask them about other parts of their life and school.