Write each student's name on a card, and do this for every student. So if you have seventy students, you will have seventy cards. I would suggest that you do this class by class. So if you teach three classes, I would invest in three boxes and in three sets of index card dividers. After writing each student's name on the card, file the cards alphabetically using the dividers, and in minutes you are done. Now, when a student is absent, pull his/her card, and on the back, you write the date of the absence and the assignments that particular student missed on that day.
You will soon learn this is a fabulous way to stay organized, and once you get in the habit of recording absences and assignments, you will know how efficient this system is. When a student comes to you to ask for his or her makeup work, all you have to do, is pull the student's card.