OCONOMOWOC, Wis.—Elisabeth Hoffman and fiancé Josh Loeser paused by a display of artfully decorated cakes and pastries while shopping recently at a Pick ‘n Save grocery store here. But after a split second of interest, their expressions faded.

“They’re not on the list,” said Ms. Hoffman, a 35-year-old interior designer and remodeler, as they pushed on to pick up chicken breast and diced tomatoes for a chicken chili recipe.

She and Mr. Loeser, a 30-year-old heating and ventilation repairman, have adopted a series of habits to make sure they buy only what they came for. They shop together, for instance, and when possible they avoid grocery carts, which come with the temptation to fill them up.

Retailers wondering what’s gone wrong with their business could learn a lot from the couple—and from other Milwaukee-area families The Wall Street Journal spent time with this fall. Observations of their carefully executed shopping plans identified what may be an endangered species in the retail landscape: the impulse buy.

A new intentionality has taken hold of shopping. Many Americans have the money and the will to spend. But they are time-pressed and deal savvy, visiting stores only when they run out of items like cereal or toilet paper and after doing extensive research on purchases online and with friends. They buy what they came for—and then leave.