Start working on your physical and dietary health. You may start off the year with 3 months where it is really hard to work out. You'll feel much better on call if you're in good shape.
Visit family members/friends you haven't seen in awhile. For many of us residency is our first "real" job where, unlike med school, you can't just pop out of town for the weekend to visit Uncle Joe in Cleveland. It is a time in your life when your family will be going about their lives largely without you around.
Take care of simple stuff like organizing your paperwork, throwing out surplus crap around the house, getting the car tuned up, buying some new underwear.