This would make a great procedure (Harry Wong). Count to five or hold up one finger at a time when the class needs to refocus. Discuss what occurs for each number at the beginning of the school year and eventually the reaction will be automatic.
I'm all for making kids responsible and this is a good way to do it. The things they missed are all in one place. It is up to them to get their materials. This teacher has a lot of great classroom organization ideas.