I try to get out on the river regularly, even in the winter, but sometimes the cold makes fishing unproductive, painful, and/or just ridiculous. On those days when fishing is just not going to happen without putting digits and even entire limbs in jeopardy it's good to have a few winter projects set aside. A few of these that I usually benefit from include organizing my bags and vest, organizing fly boxes, and cleaning up neglected gear like fly lines and waders.
Winter is also a great time to wrap rods, build such handicrafts as leaders?, nets, or even boats and of course there is always fly tying. I like to put together a simple list of stuff that I'll get done when it's too cold to fish and when it warms I'm usually glad I did at least some of the stuff on the list. Hopefully this never happens for most of us but in the unhappy event that we get stuck inside instead of playing fish we might as well play with our fishing stuff.