There is much symbolism in "A Pair of Silk Stockings," and because the symbols are integral with the objects necessary to the story--instead of, for example, an added adornment like an etching of the Himalayas worn on a necklace chain--they are hard to pick out, actually making the story more obtuse for that reason.
The first symbol is the $15 itself. It symbolizes both past and future: her past "better times" and a small light shed on her "dim future" making the "monster" look a little less "gaunt" for a time. Related symbols are the gloves, representing status and a remembrance of her past, and the magazines, a pleasure known from her past "better times," a time when she actually could indulge in the luxury of thought.
A contrasting symbol bespeaking her present life is her "shabby old shopping bag" and the cotton stockings she "thrust" into it. This action of thrusting away her stockings is the closest Mrs. Sommers ever gets to a negative emotion expressed toward her present life.
The gaily colored silk stockings symbolize the colors of life; the gairty, the carefree pleasure, the time for thought, time for happiness, time thinking of oneself. Hand-in-glove with this is the restaurant interior that symbolizes the better life she never thinks about; and she sees upon close examination that it is more spotless and more sparkling than she had realized. In other words, her past was more lovely and pleasing than she had realized. That life was nice and would still be nice to be part of.
At the theater she shares a laugh, a tear, a chocolate--but doesn't share the possession of a hankie--symbolizing that Mrs. Sommers is still of that class that she left four children and a marriage ago. On the cable car, Mrs. Sommers comes the closest to expressing regret for her past life--but without the gloom of negativity--when she is said to have a wish, a longing for her last moment of this reclaimed portion of herself to live in perpetuity. This wish and longing express something deeper than regret, as they are the products of clear vision, i.e., the restaurant, (and therefore unambiguous) and are without rancor.