Use your calendar as a diary. When things come to mind that you are proud of about your family, jot it on the calendar. There's also extra space on the bottom of most calendars to write notes. Then in November, go over your calendar, and create a wonderful newsletter to send to family with everyones' accomplishments in it.
I start my holiday letter on Jan 1, and update it monthly. When appropriate, I include photos. When it's time to mail the cards, the letter is ready to print out & send!