I do the same as Oberon and Bonehead- winter is good for catching up on my garden notebook/plans. I sort all the plant tags I have tossed in a box all year with date and location written on them.
I do no fertilizing, but at some point might spread some bagged mulch I never got around to dealing with. I don't cut much back, I leave it up for the birds and to help with erosion control as I live on a slope and hill.
Yep there are a few outdoor chores I can do, using my Flame Weeder, hacking away at the blackberries, English Ivy, bindweed and wisteria that come into my yard from the neighbors...
I start looking at seed/plant catalogs-these used to come in after Christmas, now they start showing up in December! It takes a long time an lots of lists to decide what to get.
I have a bunch of used gardening/botany books I have been buying over the year, intend to read them (this fall I got some on South African Bulbs, as some will be hardy here).
Clean the garage out... This year I WILL do it. I plan to put a little electric heater there so it will be dry and comfortable that day.
Like Bonehead I intend to clean up my tools this year, I actually bought some Linseed oil for the wooden handles.
This spring I got some indoor light fixtures for starting seeds in January/February.
I need to re-plan my "South Bed" as most everything I planted is 6 feet tall instead of 2-3 feet, and the "Fireworks" Solidago is turning the flowerbed into a Fireworks explosion. Anyone want some?
Oh and in December you should try "Wintersowing", this is great fun, it really is a nice thing to do in a "down" time, and then everything just sprouts in the spring and is ready to go! I often go out and looks at my containers to see if anything has sprouted yet.
Another little project I might work on (Uh oh the secret is out) I have lots of photos that I can upload into the database for Acorns. I especially think I am going to work on photos of seedpods and seeds, as these are mostly nonexistent and now that I am saving seeds I often have trouble identifying what is a seed. I found an adequate seed photo can be done with my Iphone.
MOST fun of all last year and now- I have been saving seeds, joining the seed swaps here in NGA. It's a blast, gives me something to think about and do in late summer and fall. I just finished packaging up about 40 kinds of seeds I saved! Plus when I buy a pack of seeds I almost never plant all the seeds, and I can swap the rest for other things. Now I will have all kinds of new seeds for my Wintersowing.
So this year I am not at all blue about the winter-I have a lot of fun things to do!