Well since you are allowed Santa, why not writing letters to Santa?
Or the kids could write a story about where the kids would take a magical train ride if they could go anywhere.
There are also the dice game where you roll the dice to determine what you will decorate on the scene. I wonder if you couldn't find or make one where the kids decorate a train.
As a counting activity they could make polar express trail mix - have them add a predetermined amount of marshmallows, goldengraham cereal and chocolate chips to a baggie to take home as a treat.
Pin the nose on the caribou or smoke on the train?
If all the kids celebrate, they could connect the rings for a countdown to Christmas(a ring is torn off each day). It could be connected to a bell or reindeer.
The could make a train or winter inspired book mark for all the books they will read over the Christmas break.
You may try looking on pinterest too. There are lots of hidden treasures on that site.