We always fill our freezer to the top in the fall. Some of the last extra space can be put to use with a gallon or two of apple cider. Cider freezes very well of you pour off a cup or two to allow the liquid to expand. the last berries of the year can be frozen by spreading them in a single layer on a cookie sheet. After they are all frozen individually, pour them into your freezer bags. This way they will not become a solid mass of colored ice, which is less appealing to the eye and harder to use.
During the winter, we find, produce, meat, cider, etc. are used regularly and the freezer is pretty well emptied by spring. This empty space seems like a great waste so last year my wife and i started to take advantage of the extra space by storing a few baked goods.
We soon realized that during the winter one tends to bake a lot. The house is cooler and the addittional heat of the oven is helpful. During the hot summer months we never, or at least rarely, bake a pie, or our own bread.
Now, during the colder months, whenever I am going to make a pie, I make two instead, and we freeze one. the little work of making an extra pied is rewarded during the summer when it is thawed and eaten. It is almost as easy to make three loaves of banana bread as it is to make one, and then I can freeze two loaves for later.
Freezing small quantities is often helpful for other reasons. No one in my family likes kidney beans except me. So one day I cooked a pound of kidney beans, divided them into six small packages, and froze them. Now I can heat up a single portion any time I desire.
Making a whole cake for my family seems to be a waste because we never eat all of it. Now we usually make a bunch of cupcakes and any that are not eaten right away are frozen. In this way we are slowly stocking up for the summer, not just for the winter.
To the question of what to freeze my answer is that if you like to eat it, try to freeze it. Cream pies do not freeze well and neither do meringues. Pastry seems to last well and so do cakes, breads, and even pancakes. Stews, chowders, and sauces which requires long periods of cooking can be made during the winter and frozen.
Keep in mind that a freezer will dry out anything that is exposed, so seal foods air tight to avoid disappointments.
Two books that have helpful information on freezing are "Joy of Cooking," by I. Rombauer and M. Becker (Bobbs Merrill) and "Stocking Up," edited by C. Stoner (Rodale Press).