Do this whenever you have new material to add. If there are some items you are not sure if you need, save them anyway. At the end of the year if you decide that you don't need some items, you can throw them away then
Thinking ahead: To avoid a last-minute scramble during your kid's senior (and very busy) year, start a photo file that includes pictures of your child (from birth through high school) and his/her friends, plus pictures of your family. These can be used for graduation announcements, invitations, or collages if your kid has a graduation party.