It's strange to think now, but there was a time when unescorted women were not especially welcome in restaurants. Many were chiefly the haunt of men who often brought showgirls and other women of dubious integrity in the evenings, and the presence of a potential spouse could lead to difficulties; during the day, women were hardly seen at all.
If a lady were to feel hungry while in town during the day, her only recourse was to purchase a sweet at a bakery, or similar establishment -- having an appetite at all was considered coarse. In the 1890's, however, this began to change with the introduction of women into the workforce and the popularity of shopping at department stores as a recreational activity. To accomodate these women, a new kind of establishment was set up: cheerfully well-lit with light-colored or mirrored walls (to signify modernism, and distinguish it from a dark-walled barroom or "lobster palace"), with no liquor in sight, where women could rest and/or congregate and the food, far from the hearty chops and ale of male interest, was designed to tempt even the daintiest of female appetites. Hidden away in department stores, country clubs, and other female haunts, "lunching with the girls" came into its own during Prohibition, when the bars connected with hotels were forced to close -- replacing them with lunch or tearooms seemed only natural. During the Depression the emergence of many womens' clubs and associations helped, too...many women cooked and served this kind of food in their homes, as a suitable precursor to a hand of bridge, or a lively discussion of civic beautification.
The food associated with this activity was usually described as "light" -- in color, anyway. Most of it was based on cream, or mayonnaise, gelatin, bread, and cake. Cream soups, sauces, and the like were favored over darker, meat-based gravies, light-colored inside leaves and stalks of vegetables over their darker fellows, and strong flavors -- onions, peppers and garlic shunned as if they were poison. (Oddly enough, curry was a favorite flavoring -- but only the mild masalas were used.) The menu was usually soup, of some creamy or exotic flavor, hot or cold (jellied was a nice touch), salad (which could also be jellied, but was often based on mixing various foodstuffs with mayonnaise), and sandwiches (which had their crusts trimmed, and were cut in small pieces to facilitate neat eating). Fruit, cut up and artfully arranged, was a given -- here again, bananas, peeled apples, and pineapples were favored over peaches, plums or berries. Green salad was sometimes seen, but not favored -- too messy!
The Cadillac of Ladies' Lunch was hot food -- meat, fish, or the like, in cream sauce and served over a puff-pastry shell as "Lobster Newburg" or "Chicken a la King" or any number of other variants, rice and/or egg dishes were also favorites. Novelty dishes abounded -- one fad of the Thirties brought breakfast food (cereal or waffles) to the lunchroom, and another, popcorn served with fruit and a glass of milk (although it could also be eaten like cereal or used as a salad garnish) and naturally, almost any kind of food that could be colored and/or formed and/or given an exotic (but still polite) flavor. Alcohol returned in the form of what would now be called "girl drinks" about then, but was never a rule -- serious drinkers found the prospect of weak frothy drinks disheartening, while less bibulous types stuck to coffee. (Oddly enough, bakery shops in the 19th century often served cordials along with the sweets, which were one of the few ways a lady could nip a little on the sly.) Breads were an exception to the "light-colored" rule -- the bread basket was a veritable cornucopia of light, dark, fruit and nut, and various other forms of bakery, as were cakes, which also came in a myriad of varieties.
Ladies lunch isn't seen much now -- most ladies are working, not shopping, during the week, and few women seem to have the taste for leisurely consumption of several thousand calories -- it's as if the spectral ladies' lunch in Ray Bradbury's "There Will Come Soft Rains" has come true. Still, the food is excellent, in its way -- perhaps with the new drive for women to organize themselves, it may yet return.