"Everything you need to know about buses in Lancaster and Morecambe over the festive period" is the title of the leaflet produced by Stagecoach to advertise their services over Christmas and the New Year. You can read a copy via this link
As in previous years, services will close down early evening on Christmas Eve and New Year's Eve and there will be no buses at all on Christmas Day. Boxing Day (26th December) sees a special daytime service operating on the following routes:
2A University - Lancaster - Heysham (Combermere Road)
3A Lancaster - Bare - Heysham (Combermere Road)
6A Lancaster - Morecambe
40 Morecambe - Lancaster - Preston
55 Lancaster - Carnforth
Full timetables are in the leaflet
However, despite its title, the leaflet doesn't really tell you everything about Lancaster's bus service over Christmas. Service 555 Lancaster - Carnforth - Kendal - Keswick will be providing a Sunday service on Boxing Day, but as it's operated by a completely different part of Stagecoach (known as "Kendal Depot") there is no mention of this in the "Lancaster and Morecambe" Christmas leaflet.
If you want to check, you need the "Kendal and the Lake District" leaflet, which you can see here.