“There are families not eating at the end of the month,” said Stephen Quinn, executive vice president and chief marketing officer at Wal-Mart Stores, and “literally lining up at midnight” at Wal-Mart stores waiting to buy food when paychecks or government checks land in their accounts.

    Among the steps Wal-Mart is taking to address the changes in shopping habits, Mr. Quinn listed an overhaul of the retailer’s private-label brand, Great Value, which is promoted in commercials describing how families can fix dinners with Great Value products “for less than $2 a serving.”