I'm jealous! I love school auctions (let me know of any future school auctions). You could use it for a weekly guide (leaving off Sunday). Maybe to do lists for days 1-6. Or cards with the menu planned for those days. Or letters you plan to mail on a particular day of that week. Those who homeschool could put their child's daily school chart in each slot. If you put the 2 of yours together, you could have a slot for the 12 days of Christmas with an activity listed for each of those days. Maybe you could have it out on piano lesson day and kids can pick a trivia question to research before their next lesson (1-6 could indicate level of difficulty). They could get a small prize or piece of candy for bringing the correct answer the following week. Or how about a place to put a Bible verse to memorize each day (day 7 can be review of days 1-6).
Christmas card holder - to display all the Christmas cards you get in the mail.