Another vote for Fellpack, now located at bigger premises around the corner from where it was when Grace Dent reviewed it for The Guardian. The Round burger restaurant by the same folk in also excellent.
Walla Crag is a nice walk if the weather smiles.
Whinlatter is fun and has GoApe, cycle routes, short walks and a good cafe. We travel up in spring and summer so you may need to check if it there are buses to it at this time of year.
The 555 Lakes bus got a mention as a great bus route in last week’s Guardian. Can facilitate a trip to Grasmere, Windermere etc.
Cockermouth has Wordsworths house and a brewery tour. Nice cafes too.
Markets - I don’t know about Christmas, but the Saturday market is really good.
Ye Olde Friars of Keswick sweets, chocs, chutney, jam - kitsch classic. Keswickian fish and chips 👍🏼
We have mostly visited by train and usually go to Penrith and then taxi or bus to Keswick.
Penrith is worth a look - has a castle. The postal address of the Center Parcs is Penrith, but it’s a bit out. I’ve not been there though as not really our sort of thing. Rheghed is just outside Penrith, not been for years. I think it has an IMAX.
The foodie capital of The Lakes, is Cartmel. So not really The Lakes. Between Braithwaite and Whinlatter is The Cottage in the Wood. Tasting menu, Michelan type stuff in the same kinda territory.
Bassenthwaite station is a former rail station where they do afternoon tea and murder mystery events. Also recommended by Grace Dent in The Guardian