I have found it works for me to ensure the students that, just as I listen to what the sub has to say, I equally listen to what they have to say. Once they learn that their voice has value, I get less game-playing and more responsible behavior from them. This pays wonderful rewards. The students know that I will listen to their version of the day, that if the sub was 'weird', I will listen, and that if the sub leaves good notes (which they most often do), that I will give the class the good feedback. They also have come to understand that a sub cannot always be the source of informational help that they might wish. This does not make them a bad or stupid person. Consequently, I feel comfortable with having a sub there. Last year I had to be gone for surgery and I encouraged the students to e-mail me if they needed help. As a result, I now encourage students to e-mail me any time they have a concern about a lesson, an assignment, or whatever.