Merry Christmas, I suppose, if you like that sort of thing. The nice thing about working at the library is they don't inundate you with "Christmas music." I feel a lot more of the Christmas spirit when the night is actually silent.
Stuffed in your mailbox, because Donna wants to avoid any embarrassment. She really, really hates Christmas shopping.
Yura: Girly shampoos and such. Because Yura is still a mystery to Donna in many ways, and shampoo/soap is the ultimate generic girl gift. Donna is kicking herself repeatedly for not having any better ideas.
Karolina: A giant X-Files poster. She was tempted to keep it for herself, but doesn't want to look like a stalker. >.>
Negi: A book on learning to do magic tricks. It seemed like a good idea at the time.
Rose: Some of the pictures of Mulder from when he was staying with Rose before. Donna hopes that, even if it doesn't jog a few memories, she'll at least enjoy them.
The Doctor: A mug that says "CERTIFIED GEEK" on it. Because it is trufax.
Mulder: A book on unsolved mysteries in the City. She wasn't going to get him anything, because dude, awkward, but it was too perfect to pass up.