Haven't thought too much about this 🤔. The ones who most definitely celebrate Christmas are Eddy, Moriah, Trent, Dave, Cliff, & Pat. So I'll answer for them.

Eddy - For the Christmases he has been able to enjoy at home (being a retail worker doesn't always guarantee that), he just enjoys relaxing and having some time for himself. A warm fire and a hot drink helps with that too.
Moriah - Decorating her space with gaudy Christmas decorations.
Dave - Making batches of his famous peppermint hot chocolate for his loved ones to enjoy.
Pat - Getting smashed on boozy eggnog & seducing cute boys to kiss him under the mistletoe.
Cliff - Secret Santa. He likes coming up with thoughtful gifts and is very good at it.
Trent - He loves the general idea of gift exchange. He goes a little overboard with his purchases for his loved ones, sometimes.