I had cardboard boxes I bought at the craft store last year, and bought a few more to make 24 of them. I got out a bunch of letter sticker sets and dated all the boxes, then cut different lengths of ribbon (yes, I have a lot of ribbon on hand), tied the boxes to those, and tied them all up on a long piece of ribbon across the windows in the living room.
I split the days up into activities, toys, and treats, and I only did 24 days, not 25, figuring they were getting plenty of presents on Christmas anyway. We have activities like driving around looking at Christmas lights or watching a Christmas movie while others are craft projects like this cute popsicle stick nativity set we just did. I'm excited about all the fun art projects I've included--I just have to make sure to make time in our schedule in the evenings to actually do them. I know some will get pushed back, but I'm okay with that. I tried to coordinate all the activities with my calendar so we don't have too much going on on one day. I made sure the last three days before Christmas were treats or gifts because I know I'll be busy with other things on those days.
The kids have been loving it so far. It's the highlight of their day when Ben gets home from school and they get to take a box down and see what's inside. I have a feeling I'll have to make one next year whether I want to or not!