At the end of the day fill out the slip for students who were absent from your class(es). While it may seem like a little more work for you while you're filling them out, it saves A LOT of time when students return to school and are asking you for all their make-up work (usually in the middle of a lesson while you have a billion other things on your mind). There is an assigned spot in my room where the slips and any materials are left for returning students. It is their responsibility to come in and get the information. At the beginning of the school year I often remind students who were out to go check for their slip, but as the year progresses I leave it up to the student to be proactive and responsible to check for their own slip. If students do not pick up the work and miss out on assignments you then have the concrete proof that the student never picked up all the materials. Parents LOVED this system for make-up work.