Like others have said, July-September is back to school - this is like Christmas at Best Buy.
I worked for Office Max for 2.5 years, worked 3 BTS there and at Staples for 1.5 years - just 1 BTS there. Never worked at Depot but it should be similar since they're both office supply stores. Try to get into the Copy Center - that is without a doubt, the easiest job there. You usually have customer jobs to fill and run so you're not stuck doing bullsh!t busy work like stocking the pen aisle or something lame like that.
For the most part - it's like any other retail job - just stock stuff, help customers, zone up at the end of the night, etc. The thing that will either make or break your experience is the managers - either they'll be great and kind and caring, or they'll be dicks in one way or another.
Either way - it's not the most glamorous job but hey, it helped put me through college.