Bottle of vitamin D if you're headed up at all during the dark season (Right now, mid january, they're probably getting a few minutes of twilight per day)
Bring a good sense of humor, patience, and be willing to get out of your room and socialize. I've spent a reasonable amount of time in the arctic, and everyone who doesn't enjoy their time is crooked because they spend their off hours crooked in their rooms watching movies.
And take EVERY OPPORTUNITY YOU CAN TO PLAY TOURIST!!!!! If the opportunity comes up to go a fair distance, say Tule, or Eureka, TAKE IT! If the opportunity comes up to go fishing, go to crystal mountain, whever, DO IT! Even if there's no opportunities that come up, make friends with the EC people and visit the GAW lab, make friends with the MET tech and watch the plane land from the the shack, ask a trucker (Probably civis now) if you can come out for an hour or two while plowing, JUST GET OUT OF THE DAMNED BUILDING!!! Also, take whatever precautions are required when you are leaving the building...
Plus PT kit, there's two well equipped gyms, regular floor hockey games. If you're headed up in the summer, take some fishing gear, tackle/cheap rod. There is/was a good supply on station, but it doesn't hurt to bring some extra.
If you're stopping in Thule on the way up or down, joining instructions should tell you to take American cash, they do accept credit cards and debit, but bring enough to cover the cost of the hotel and breakfast ($60?) just in case (If nothing else, it's nice to be able to tip the drivers in Thule with money that's useful to them... it's not mandatory, but they deserve it... I felt bad when I was there the summer... one of their drivers did a fantastic thing for us, wanted to tip him, only had Canadian cash)