Hopefully by now you have raked up lots of the fallen leaves and made a compost pile. Compost is the best thing for the garden, and by using non-protein food scraps and leaves, it is a great free resource.
Most of the herbs can be planted now:
Oregano, rosemary, sage, thyme, cilantro, dill and fennel. Cilantro and dill should be protected from the freezing temps. I cover everything.
Asparagus, Arugula, cabbage, chard, spinach and lettuce can also go in in December. And you still have time to get your onions in.
Strawberry plants can be planted throughout the month, and should be well mulched. It is also time to plant bare root blackberry plants.
Remember to water well before a freeze, keep the garden well mulched, and for sustained or hard freezes, cover with row cover, sheets, or plastic.