As ever, we'll be having an employee-only Christmas lunch on site. There is a school within the grounds; that will have closed, and we'll use their dining facilities and staff.
Various departments will arrange their own Christmas festivities too - the building I'm in has arranged an evening meal for staff and select senior management

Maybe a drinks party somewhere as well - glass of wine and nibbles.
Presents - not a lot really. I don't exchange with anyone else in the office, as I work very much on my own. Maybe a bottle of something alcofrolic from my boss though!