My favorite tradition from growing up was about presents. My family always saves and reuses wrapping paper, so picking up a gift to open sparks memories and conversations about Christmases past. And instead of gift tags, we use old Christmas cards as labels. These were also reused, so one might have the "to" and "from" crossed out and rewritten twenty times all over the card. (My parents had a silent and loving battle over that card every year - it was a triumph to get to it first.) Then, on Christmas morning, the youngest child present chooses something from under the tree for someone else to open. We all watch that person open the gift, and they pick something for someone else. Christmas goes on for hours that way, with music playing in the background and lots of hot drinks going around. Lovely.
My favorite modern tradition is the Christmas curry. When my husband and I met, we were both working in Japan. When we weren't able to do our traditions from home, we decided to do something entirely different that we loved. Christmas dinner was always pork vindaloo, fancy rice, naan, popadoms, raita, kachumba, maybe some onion bhaji. Now we live in America and have family stuff on the day itself, so we save our Indian feast for Boxing Day when it's just us. Bliss!