More of a Soil & Mulch forum question or one for the Vegetable Gardening forum and you'll find several discussions about this on both those forums.

But if a cover crop cannot be planted then the usual recommendation is a several inches thick layer of a good organic mulch of some kind. Chopped leaves is common and very beneficial for the soil, so is straw or old hay. Even unfinished compost - with or without added manure - can be spread over the soil and let it continue to decompose in place till spring.

Dave

I have wanted to get burlap coffee bags from the local roasters to cover a few select beds in the kitchen garden.
Never have as of yet, but I hear they are free and plentiful (at least where I live).

Granted, this adds no nutrients to the soil as would a cover crop or even a thick mulch, but is an excellent weed barrier and can be easily pulled back in the Spring to provide access for early plantings.

I put a layer of straw on my beds while they are resting. It keeps the soil from compacting over the winter. I also use it as mulch between/around many veggie plants while they are growing. Keeps the weeds out and the cats from using my raised beds as jumbo litter boxes. ;)

Kathy