SOUP!
I love soup in the winter. I used to just make traditional vegetable or chicken noodle, but have expanded my soup menu to include a couple dozen varieties. You can buy the ingredients in bulk and either make in bulk to freeze or just stock up (pardon the pun...) in bulk. Most soups are veggies and stock, so ingredients are very inexpensive.
I also do salads in the summer and make crazy combinations. make my own dressings or use just simple liquids like just vinegar or fresh juice.