Probably some last minute trips for Christmas shopping, emergency purchases of little things like parsley or more wine or icing sugar or toilet paper. I speak from sad experience when I say it's nice not to run out in the middle of Christmas afternoon.
We do last minute wrapping of gifts to each other and they are set out under the tree.
Then preparation of a few things I make ahead like cranberry sauce, stuffing, tiramisu, and the dessert for later in the evening (most likely a baked chocolate pie).
We get dressed up, and go to Mass at 6, though we may go to midnight Mass this year thanks to one family member's work schedule. Normally we pick up a huge pizza after Mass and go home, eat, have chocolate pie, coffee, and open presents from each other and from family and friends. This leaves the space under the tree ready for Santa Claus.
After I persuade them all to go to bed for the love of puppies I rack my brains to remember where I put everything and arrange the piles under the tree and I fill their stockings with German chocolate coins and Santas from Aldi.
I am usually working until at least the day before Christmas Eve, but where I live Christmas Eve is basically a holiday unless you work in a hospital or security/army, etc. or public transport. This year DD4 (my only child left in school) will only get out for the Christmas holiday on the 23rd December though she could be out on Thursday depending on her exam schedule I suppose.