There are several factors that should be taken into account over this period:
Introduce rest days into the schedule, avoid prolongued high effort work-outs (particularly if feeling fatigued), short fast sessions on the track are good to keep you sharp (e.g. 10x400 off 60 seconds), easy jogging is good. 4k time trial (at race pace) 9 days before the race is good for testing your speed , and sharpening up - it's short enough that your body can recover quickly. In between runs, ideally you should be resting up (stationary), rather than playing golf in the rain or going hiking up Mount Brandon :-)
Weight reduction is an effective way of improving your marathon result. Each kilogram of extra weight carried around can cost up to 2 minutes on a marathon time, so it is helpful to shed any extra kilograms (not that marathon runners have much extra weight to spare). Since this weight reduction has to occur during a period of rigorous training, it needs to be executed carefully over several weeks.
It's about being healthy and choosing the right foods, rather than going hungry. For example, my approach is to cut out alcohol, fizzy drinks, processed foods that are high in fat, desserts and sweets etc in the month leading up to the marathon. I try to eat mostly unprocessed fish, chicken, a variety of fruit and vegetables, wholemeal carbs (w/m pasta, brown rice, Weetabix, brown bread). I just drink water most of the time. For snacks, stick to healthy fillers like wholegrain crispbread and fruit.
Don't get me wrong, diet restrictions are not fun, especially not sitting in a pub drinking pints of water while your mates enjoy pints of Guinness. But it seems like a waste to train so hard for months, and then to handicap yourself by carrying extra weight around on race day, when it can be shed by simply cutting out treats for a short while. Treat yourself with tasty fruit selections. Can't wait to eat a chocolate bar next week. Mmmm.
I have reduced my weight over four weeks from 67kg (normal peak training weight) to 65kg race weight. After the race my weight will naturally return to about 67/68kg as I indulge in the much anticipated post race blow-out!
As you reduce mileage during a taper (last week or two before the marathon), you will not be burning as many calories. So at this stage you should naturally reduce the size and frequency of meals as well, otherwise you're probably eating more than you need to.
Carbohydrate loading begins three days before the marathon. Choose foods for lunch and dinner that are high in carbohydrates (e.g. pasta, potatoes, rice, etc.). Don't neglect fruits, vegetables, and some protein sources though. Avoid fats.
Drink lots of water, particularly in the last few days before the race when you are trying to fully hydrate yourself (you should be already hydrated when you wake on race day). Water helps the body to absorb and retain carbs.
Stick to foods that are tried and proven.
Get lots of sleep, and lots of time off your feet, in the last week leading up to the marathon. Sleep helps your body to operate better when it is working. It also helps you to recover from the training. Most top runners sleep for 9-11 hours per day.
Rest (and nutrition for that matter) is also very important for avoiding illness such as colds and the flu, which are easy to pick up during the peak training stage, or the taper.
Try to remember that the work is done now, all you have to do is show up and give it a crack. Trust in your training. If you have down the yards in training, then it'll stand to you during the race. The last 10k of the marathon is supposed to hurt, so there is no need to fear the pain. The pain is only temporary - later you'll be enjoying the pints/steins plus chocolate, pizza etc and will have forgotten about it (until you try and walk to the bathroom). While the pain drifts from memory, the sense of achievement lasts.
Here is a more comprehensive guide to tapering for marathons: