If there isn't too much snow on the ground, you could clean up fallen limbs and branches. We had a winter a few years back with a lot of ice storms, and decent 40 degree weather in between. I kept pretty busy cutting up big limbs that fell. Even a few rotten trees that came down completely. You can also trim trees. Those telescopic chainsaw attachments for weed whackers are great for trimming.
We line up tree work in the fall and put it off until the winter. The last few years we have kept very busy cutting trees, fallen limbs and clearing lots. This year there is too much snow on the ground to get out and do the work. Now those customers are upset that we havent done there jobs yet. Seems you can't keep anyone happy. But we usually try to keep busy through christmas doing cleanups and then we start doing tree work and brush clearing, firewood delivery, fixing up gravel and stone driveways. Just My two cents