To get teachers, parents and kids in the mood to buy back-to-school supplies, Office Depot is running a $500,000 "Go Back Smarter Instant Win Game." Customers who make an Office Depot purchase through Sept. 5 get a coded receipt, which they can enter at www.school.com. The retailer chooses 50 general winners each day, who get $100 in Office Depot gift cards, as well as 10 teachers, who receive a $500 gift cards. (Teachers typically spend $500 of their own cash to stock their classrooms each year, the chain says.) The promotion is a partnership with Sanford, a Newell Rubbermaid brand that makes such products as Sharpie markers.