In the old days (and in Richard Scarry books), food shopping was a multistore marathon: the butcher, the baker, the greengrocer. Now the options are different: Should you go to a grocery store, a discount club, or a farmer's market? Marketing professor Teck-Hua Ho at the University of Pennsylvania says it makes financial sense to divide your shopping among them.

Go to the low-price outlet once a month or every two months.

Buy products in bulk or products that are never on sale at the grocery store. Buy enough to last until your next visit.

Go to the grocery store once a week.

You'll be able to take advantage of promotional sales. "Cherry-pick the items that are on sale," advises Ho. The sale items can be less expensive than what you find at the outlets, and the atmosphere is generally pleasant, he says.

Go to the farmer's market or produce aisle as needed.

Trying to crisp up Sunday's head of lettuce on Friday is frustrating, and shopping the green market is typically an enjoyable experience.