Aww, I like this thread! We had some fun traditions when my sister and I were kids - now that we're grown up and scattered around the country they've gone by the wayside, unfortunately. I can't wait to have Christmas with my own kids so I can bring them back!
First, my sister, my Dad, and I used to always go swimming on Christmas Eve (in an indoor pool somewhere, not outdoors!). I'm pretty sure this got started because we were all wound up and driving my Mom crazy while she was trying to cook and wrap presents, so my Dad would take us to a local Y or something and let us swim until we wore ourselves out. We did this every year until my sister and I were in college!
After swimming we would go to the Christmas Eve service at church. Then later we would watch the old claymation Rudolph the Red-Nosed Reindeer and read some kid's Christmas books together - even when we were too old for picture books. We would also put a "landing strip" of Christmas lights on the roof so Santa could land his sleigh, then we put out cookies and milk, and a carrot for Rudolph. We each got to open one small present, then it was time for bed.
There was always some sort of time limit in the morning (like, no getting out of bed before 6:30am) but inevitably my sister and I would be awake and barely containing ourselves by 5:30am. When it was finally time we would run into our parents' room to wake them up, then head down to the living room. My parents were pretty frugal in general but did like to go all out on Christmas, so there was always a really beautiful display. We would open our stockings, then eat breakfast - a traditional bread with nuts and cinnamon that my Mom makes every year. Then, back to presents! Later in the day we would go to see grandparents and family and have a big family dinner at my Aunt's house. Lots of great memories.