Two cents for a piece of bubble gum is bad enough, but when one store began charging 15 cents for a Halloween-sized Snickers, it was reason enough to swear off the sweet stuff for more nutritious food.

Unfortunately, not all food is as easy to give up as candy. We have to eat, after all. Enter Mary Goodwin, Montgomery County's chief public health nutritionist and "Eating Well on a Tight Budget," a pamphlet she has put together in an attempt to help consumers squeeze as much nutrition as possible from their food dollar.

While the booklet itself is available only to Montgomery County residents, we all can benefit from its universal principles. It briefly answers frequently-asked questions about correct food choices. Goodwin maintains that many people want to start eating more nutritious foods, but they just don't know how. "Start slowly," the booklet advises. "Give change a chance." Anyone who has eaten sugar on his cereal for 20 years won't wake up one morning craving whole bran and wheat germ. Changing food habits takes time.

The information "has a point of view," says Goodwin. It stresses ecology and long-range problem solving -- how to use leftovers, how to save money by making simple foods such as salad dressings -- and even advises growing herbs, vegetables and fruit trees. The booklet gives storing tips, advice about a balanced diet and a few recipes.

It also includes such advice as:

* Using your leftovers: Stale bread can become crumbs for topping casseroles and breading meat, vegetables or fish. Or it can be cut into croutons for salads or soups. Slices make good french toast or bread pudding. Leftover fish can replace canned tuna in salads, loaves, chowders and fish cakes. Leftover meats can be tossed into green salads and omelets. Leftover cooked vegetables can be added to homemade or canned soups.

* Doing it yourself: Store-bought salad dressings are expensive and making them at home is simple. Mix oil and vinegar with dry or prepared mustard, paprika, salt and pepper. Yogurt or sour cream combines with a little mayonnaise, dill and garlic for a good herb dressing.

Goodwin points out that August is a great time to make tomato sauce. If you don't have a garden, she says, buy tomatoes by the bushel to make different sauces for a homemade convenience item.

* Planning ahead: In addition to shopping with a list, plan to carry food to work and on trips -- dollars spent eating out add up in a hurry.

Low-cost foods obviously stretch the food dollar: Fresh produce in season becomes even cheaper when families combine their purchasing power to buy in bulk. Neighborhood co-ops may also offer bargains on flour and grain, cereals, nuts, dried fruit and seeds bought in bulk.

But you needn't go a long way to get inexpensive foods, nor should they take a lot of trouble to prepare. Eight items can equal dinner and get you through the supermarket checkout in a hurry.

Every kitchen should be supplied with flour, sugar, salt, pepper and shortening, butter and/or vegetable oil.

Express Lane list: Bread, cheese, milk, eggs, zucchini or summer squash, tomatoes, green pepper, cider vinegar. CRUSTLESS CHEESE PIE (4 to 6 servings) 1 cup dried bread crumbs 1 cup sliced zucchini 1 1/2 cups grated sharp cheese (cheddar or swiss) 2 cups milk 4 eggs

1/4 teaspoon salt or to taste 1/4 teaspoon freshly ground pepper

Sprinkle 1/3 cup bread crumbs in lightly greased 10-inch pie plate. Cover with a layer of sliced zucchini. Sprinkle with bread crumbs and cheese, layer the zucchini again and sprinkle with more bread crumbs and cheese. Combine milk, eggs, salt and pepper and pour over zucchini. Sprinkle top with any remaining cheese and bake at 350 degrees for 40 minutes. Allow the pie to sit for 10 minutes before slicing.

Serve pie with marinated garden vegetables and homemade biscuits. MARINATED VEGETABLES

Remove the cores from 3 green peppers and slice the peppers into strips. Core 6 tomatoes and cut them into chunks. Combine 1/4 cup vegetable oil with 1 tablespoon cider vinegar, a favorite herb that might be on hand, salt and pepper. Toss with vegetables and chill before serving.

Any Montgomery County resident can get "Eating Well on a Tight Budget" by sending his name and address to the Montgomery County Health Department, 2000 Dennis Avenue, Silver Spring, Md. 20902.