I'd say not specifically festive stuff because they'll have got all of that baked/bought and will have had more than enough of it by the time you go home and they start using the hamper.
I'm assuming you're putting your own together? How about speciality coffees/teas/hot chocolate, preserves, chutney, nuts, a small box of top end chocolates, booze if they like it. Things that are a bit out of the ordinary.
If you're wanting something ready-made, there are lots of shops that can oblige. I don't know where you're from, or where your friends live, but if you're from different areas, some of your local specialities might be nice. If I was in that position for example, I'd probably go for something from Botham's - they do some really inventive ones, including some with Whitby kippers! - or Betty's.