When I commuted weekly with SAS/BA I got to know a lot of the crew and on my last flight at Christmas I usually bought some chocolates in duty free (I asked the shop to seal the bag so it was obviously genuine and untampered)and gave them to the crew. They always seemed grateful - on one flight I saw the crew divide them out into cups and hand them out among themselves (every crew member including the captain came and thanked me which was a bit much but nice) and on SAS the crew had some and offered them to kids on the flight too.

I thought it was a nice touch considering I spent almost as much time with them as I did with my family at that time.