Christmas is our cultural holiday. We are not Christians, so the holiday has zero religious meaning for us and is strictly cultural. However, we *DO* have a winter holiday in our religion, Yule (the Winter Solstice). It occurs a few days before Xmas. On Yule, we do a family ritual and we open ONE gift each under our Yule tree. That one gift is ALWAYS our new holiday pajamas.
We wear our new PJs the night before Xmas, and while still in them, we open the rest of our gifts on Xmas day.