Obviously Christmas is a big thing at my place of employ!  There is one major Christmas lunch for all staff (we have a boarding school on the premises, so we use their facilities after the children have gone home for the Christmas break); departments can organise their own lunches/dinners as well.  Offices are decorated, but it all has to be relatively tasteful.  Gift-giving - I've got something from my two main bosses each year; as I'm really just a department of me, there's no-one else to give to/organise a Secret Santa with.

Apart from the usual regular round of services, there are all the Christmas ones to be slotted in.  Two major public carol services this year; one each on the 23rd and Christmas Eve.