I ended up buying a wooden kit advent calendar, and decorated it with my little assistant. He was very patient during the process although he did wander off before we were done.
There are little drawers to fill things with. The bigger ones are big enough for a small car, but the highlight for him has been him daily vitamin. Apparently it is far more exciting when out of a tiny box. I also picked an activity for us to do each day and that has worked really well to keep me on track for getting ready for Christmas.
Today was wrapping presents. A few days ago was making cards. Other activities were to decorate the Christmas tree, buy a special new decoration, and watch a Christmas movie (he asked to watch Paw Patrol instead). I’d forgotten about some of the activities so it’s been a surprise for me as well. I’m really glad that I went to the effort of doing it this year.