WE MAY NOT remember what we had for dinner last Thursday, W but memory holds even the smallest details of picnics long past.. It is the special circumstances that make picnics memorable: the free and easy spirit of the meal, the good or bad weather. Maybe it's remembering to take everything or forgetting the beer. Maybe it's enjoying sun-warmed havarti cheese or suffering mashed sandwiches. Maybe it's a bugless day, or one humming with mosquitoes..

Picnics involve all our senses--the more to remember them by. Who could forget discovering a quiet, beautiful cove, having a swim and walking the sunny beach, picking up unbroken sand dollars? A thermos of minty iced tea, chicken sandwiches and sweet cherry tomatoes seemed the perfect food, eaten to the gentle sounds of singing birds and surf.

One of the finest picnics in my memory happened in France. It was October; my husband and I were driving through the Loire valley. We were hungry, but had found no restaurant. Suddenly, around a turn, we discovered a little store beside the road. Using fractured French we bought wonderful, mellow cheese, white wine and a yard-long loaf of crusty french bread to supplement the ripe pears we had in the car. We picnicked beside a recently cut grain field, watching a hunter and his Brittany spaniels flush a pheasant from the amber stubble. The day was warm, the sky was blue, the food was good--a memorable picnic.

Most picnics are not so spontaneous. But a well-planned picnic has no less-memorable charm; here is a list of picnic suggestions that may be helpful.

* No matter how pretty a picnic basket, an enclosed, heavily insulated cooler chest is actually the best picnic hamper. (If you're lucky enough to have one of the old-fashioned, insulated baskets, that's fine.)

* Styrofoam chests are inexpensive, and will keep food hot or cold; ditto a well insulated ice bucket.

* For a short haul, hot food may be transported by wrapping in aluminum foil, and then several thicknesses of newspaper. This method works well for casseroles.

* It is a good idea to buy perishable foods close to the picnic site and serving time.

* If using dry ice to keep food cold, remember to put it on top of the food, as the chilling gas (carbon dioxide) is heavier than air.

* A popular substitute for loose ice in a chest is the freezer-bottle, or ice pack, which is kept in the freezer until time to travel. The cold pack is put into an insulated chest and keeps the food cold for hours. These are available in hardware stores or picnic sections of many stores.

As an alternative, make your own freezer packs by filling plastic bottles or containers two-thirds full of water (this allows for expansion) and freezing them. These containers eliminate problems caused by melting ice. Foods on ice are best protected in plastic containers with tight-fitting lids.

* Before filling a thermos with a hot or cold beverage or food, heat the inside with boiling water, or chill it with ice water. A container that is the same temperature as the liquid will retain the desired temperature longer.

* Keep your picnic hamper stocked between picnics with essentials such as flatware and napkins. If you do this, when picnic time comes, you can concentrate on the meal.

* In addition to the obvious needs--a plastic-coated or terrycloth table/ground cover, a beach towel or a roll-up reed mat; plastic or enamel plates and flatware and plastic glasses; cloth napkins to minimize refuse; can opener and corkscrew; salt, pepper and condiments; a small cutting board and a container of water--carry along damp washcloths in plastic bags and extra bags for throwaways. Insect repellent has obvious attributes.

* If your site lacks a grill, you may want to take your own hibachi, bucket-broiler or folding grill. Remember the charcoal, charcoal starter and matches. If you don't have a cooker, you can improvise with a large clay flowerpot, new or scrubbed clean. Fill it with sand, leaving enough room for a charcoal fire. Put a grid across the top, and you're in business. This improvised cooker is fine for simple things like hot dogs and hamburgers, and it's inexpensive. Be sure this pot rests firmly on the ground or other fireproof surface, and for safety's sake, remember that the rack is not attached to the flowerpot.

* Keep food properly chilled or heated after as well as during; if there is the slightest doubt that leftovers have been left out too long, or improperly stored in any way, THROW THEM OUT.

Good food also plays a part in good memories. Here are some ideas: CORNED BEEF AND HORSERADISH SANDWICH (Makes 6 to 8 sandwiches) 3-ounce package cream cheese, softened 1 to 2 tablespoons mayonnaise 1 teaspoon dijon mustard 2 tablespoons chopped parsley 1 to 2 tablespoons well-drained prepared horseradish 12 to 16 slices dark or rye bread Corned beef, thinly sliced

Combine cream cheese, mayonnaise, mustard, parsley and horseradish and mix to create a smooth spreading consistency. Spread a thin layer on slices of dark or rye bread. Top with thin slices of corned beef. Serve with dill pickles and beer. CANTONESE-STYLE TUNA (Makes 2 to 3 sandwiches) 7-ounce can tuna, well-drained 4 tablespoons chopped chutney 3 tablespoons minced green pepper 3 tablespoons minced scallion 1/2 cup mayonnaise 4 to 6 slices white or raisin bread

In a bowl, flake the well-drained tuna. Mix in the remaining ingredients and blend thoroughly. Chill in a covered container. Serve on white or raisin bread. REVIVER (8 servings) 4 cups rich chicken broth 3 cups clam broth 3 cups water 2 tablespoons tomato pure'e 1 tablespoon chopped parsley Dash hot pepper sauce 1/2 cup dry sherry

Combine chicken broth, clam broth, water and tomato pure'e in a saucepan. Heat and simmer, about 15 to 20 minutes. Remove from heat, stir in the parsley, hot pepper sauce and sherry. Pour into preheated thermos. MIXED BEAN SALAD (8 to 10 servings) 2 cups cooked kidney beans, drained 1 1/2 cups cooked garbanzo beans, drained 1 cup cooked green beans, drained 1/2 cup chopped celery 1/4 cup chopped scallion 1/4 cup chopped parsley 2 tablespoons chopped pimiento 1 cup french dressing 1/2 cup small cubes monterey jack cheese (or 1 cup cauliflower florets)

Place all ingredients except cheese into a large container with a tight-fitting lid. Marinate in french dressing overnight. Drain, toss with cubes of cheese (or cauliflower florets) and pack for traveling. QUICK PATE (4 to 6 servings) 1/2 pound braunschweiger (smoked liverwurst) 1/2 cup sour cream or mayonnaise 1/2 teaspoon worcestershire sauce 3 to 4 teaspoons grated onion 2 to 3 tablespoons cognac Dark or rye bread or crackers for serving

Cream all ingredients together or put in electric blender. Put into container with tight-fitting cover and chill. Spread on dark or rye bread or crackers. CHEESE AND BEER SPREAD (Makes 8 sandwiches) 2 cups shredded cheddar cheese 4 tablespoons butter, softened 1/4 cup beer at room temperature Dash hot pepper sauce Dash worcestershire Dark bread for serving

Combine all ingredients and mix until smooth. Serve on dark bread. Carry in cooler. LOUISIANA BASTER (Makes 3/4 cup) 1 teaspoon dry mustard 1 teaspoon salt 1/4 teaspoon garlic salt 1/4 cup vinegar 1/2 cup salad oil 1/2 teaspoon hot pepper sauce 1 tablespoon molasses (unsulphured)

Combine all ingredients in a saucepan and heat before using. At picnic site, grill cut-up chicken over charcoal, basting with this sauce.