Extending your vegetable production well into the fall & winter months.

There are various ways to keep a plant producing for you longer than the usual summer months.  You may have noticed at the end of the warm weather, some plants start to look done in, not as vibrant as they were.  The cooler temperatures and shortening days will tell them it’s time to quit making food/seeds.  Your goal is to provide the plant with summerlike conditions longer to keep it producing.
If you own a greenhouse, put some of your plants in pots and move them into the greenhouse when the weather starts to cool off and give them a good feeding of fresh compost or vermicompost.  Option: you could keep watering it with some fresh brewed compost tea during its indoor production season.   Add a grow light at the top of your greenhouse to emulate longer days.  Remember that tomatoes do need some darkness and slightly cooler temperatures at night to produce good fruit.  You are trying to imitate nature at the peak producing time.  Add heat if your climate gets too cold outdoors to warm the greenhouse.
If you have not planted some of your vegetables in pots, you can pull up a whole tomato plant, roots and all, and hang it upside down from the rafters of your greenhouse.  This method does not produce as long as the potted plants, but will surprise you with how long it goes on, enabling the plant to turn all the green tomatoes red until you harvest them.  Option: try doing the tomatoes both ways and compare the taste, time span and trouble each takes.  A lot of other vegetables can be done the same way with great success.  Some of the best vegetables for growing in pots so you can move them into your greenhouse are:
Tomatoes (of course)
Eggplant
Onions
Potatoes
Green onions, chives and most herbs love it in pots.
Flowers
Peppers
Bush type squash
I’m sure I haven’t listed everything, but you can experiment with others.
Another way to eat your own produce year round is to grow with hydroponics.  If you already use hydroponics, you know how easy it is to have all the vegetables you want year round with succession planting.  If you are not already using hydroponics, you may want to try it out using one of 4 season greenhouses.com’s tabletop hydroponic plant systems during the winter months.  That would be summer months if you live south of the equator. 
How To:
Extend you gardening season…

If you have a greenhouse that you start your seedlings in, you can move your plants back into that greenhouse when the days start to cool and your plants will keep producing much longer.
Place a greenhouse blanket over your greenhouse to maintain temperatures during the cold months.
Heat your greenhouse if the temperatures drop drastically.
If you do not have a greenhouse, you can create a mini greenhouse effect by covering some of your plants, especially at night.  Tomatoes do not like to get a lot of cold rain, so a simple opaque poly panel above them will work as long as it does not freeze.
To protect your outdoor plants from freezing, cover them with whatever you have on hand.  A bucket, plant umbrellas, blankets, tarps, old quilts have been used in the past.  A cardboard box works well.  Put a rock on top of it if it gets windy where you are.
Water towers (those funny looking things that insulate with water in them) are good.
Buy a portable shelter from 4 seasongreenhouse.com to place over the garden spot or a portable greenhouse that can be moved over your plants.
Water your plants at the roots if you expect a mild frost.  The moist ground helps to insulate the roots from freezes.
Row covers that are plastic or fabric, wooden shelters and any other thing you can think of, like a burn barrel, all will help to insulate your plants from early frosts.
These methods are especially good for an unexpectedly early frost.
Be sure to uncover your plants as soon as the sun hits them.
Sometimes a mulch piled high will insulate your plant enough to get them through an unseasonable frost. 
Give your plants a second wind with a judicious dose of compost or vermicompost.
Warm the water in a can placed in a warm or sunny spot before watering your plants with it.  Consider a water barrel painted black to heat water in passively.
Cover entire rows of vegetables with straw.  You can place bales along the sides of the row and sprinkle loose straw over the plants between the bales.
Plant cool loving vegetables later in the outdoor season that will thrive outdoors even when the temperatures drop a lot.  These would be the same seeds you planted real early, like snow peas, carrots, turnips, onions, chives, beets, parsnips, celery, celeriac, greens of all sorts, parsley and many other herbs.  Most of the root crops will keep well in the ground and actually grow on the sunny days with just a heavy mulch around them.
Start new seeds indoors or in the greenhouse and garden indoors.
Place wind breaks around your garden to cut down the chill factor.
Plant a wind break of evergreen shrubs or trees.