Shop when you are in a hurry.
This works well not only in keeping your overall expenditures down but to force the decision. My daughter can shop for days on end for a prom dress. But when it is the day before and the mall closes in an hour. The decision is made and we are out the door. Since many of the food store are open 24/7 it is up to you to create some deadlines. Pick that hour between dance and Girl Scouts.