Make suet balls and hang them in the mesh bags in which oranges and onions are packaged. Cut attractive shapes from paper plates, spread them with peanut butter and bird seed and hang them on your tree. Don't forget to put out some fresh water for the birds, also. Put together a feeding station for the squirrels so that you can watch their antics through a window. Check the seed catalogs or local nurseries for flower bulbs to force during the winter.
Amaryllis are pretty.
So are crocuses and narcissus. You can also force a branch from a flowering bush like pussy willow and forsythia in a bucket of water. Okay, this is not a garden or outdoor activity. But, it is a fun thing to do during the winter. One of the cutest candles I ever made looked like an ice cream soda.