I quite enjoy a good old Christmas Carol around this time of year. A few years back, Geoff Whitehorn wrote an article in the winter edition of the excellent Guitar Technques magazine that included a rock or blues track (I forget which). Taken by the festive spirit, he inserted a piece of a Christmas carol into the solo! I thought it sounded pretty cool and not at all out of place. Quite subtle, some folk would not even notice it. I think the passage he used was from the carol "God Rest Ye Merry Gentlemen" (I could be wrong), which was, I think, all pentatonic notes.
Similary, Eric Clapton once quoted a Jazz classic (for his manager or a friend, a Jazz fan) in a Cream solo. I think the passage was from Blue Moon.
BTW I found this book to be an excellent source of easy to play Carols:
USA: Christmas Songs for Beginning Guitar: Learn to Play 15 Complete Holiday Classics
UK/Europe: Christmas Songs for Beginning Guitar: Learn to Play 15 Complete Holiday Classics
I bought it for soloing ideas but actually ended up instead playing the songs through on my acoustic guitar - and was pleasantly surprised to find that I could play them all. There is finger picking tab & chord charts - I used the former. The songs (the author choose most of my favourites) are so familiar, I haven't needed to use the accompanying CD at all. Excellent.