Summer time is great long hot days and cool nights, and you can grow so many different varieties of vegetable outdoors, but you need to plan ahead for the cold winter days, if you want to have freshly picked vegetables from your self sufficient property in the winter time.
Where you live in the world will have a big impact on vegetable varieties that can be harvested in winter, some countries will have mild winters like we have New Zealand, some countries will be just to cold to sustain any growth.
The more favorable salad varieties that you crave in the summer like tomatoes and watermelons are not feasible in the cold months, you need to look at the less traditional and not so favored varieties of vegetables like Broad Beans, Asparagus and the Onions and shallots while not varieties that can be consumed by themselves they can used with other forms of food to brighten the flavor and add to the dish.
Broad Beans can be planted in the autumn and provide a good harvest come winter, varieties like Aquadulce Claudia and Super Aquadulce are great for planting in the autumn time. Asparagus varieties can be planted in the autumn like Ariane and Guelph Millennium although there is a two year wait to harvest them, Garlic is an easy crop to grow for winter and can be stored when harvested for use later on.
Onions and Shallots are another vegetable that can be harvested in the winter and also stored for later use, Lettuce can be planted and harvested for the cold winter days although this vegetable would suit a greenhouse better when grown through the winter, Spinach and cabbage can be planted in the winter for an early spring harvest, as long as there is not to much frost, again would suit a greenhouse but grown outside in mild winters.