When we're planning our shopping conquests, I think we often forget office supply stores. To be honest, most weeks there isn't much to pull me in there, but sometimes, there is a deal you just can't pass up.
To start, you should sign up for Staples' Rewards program. It's free and there is no annoying key tag to carry with you. They'll give you a card for the account but I never take mine because they just look you up by your phone number. A few weeks ago, they had a deal on batteries: Buy a 20-pack of Duracell AA or AAA batteries for $9.99 and get $9.99 back in rewards. We go through batteries like socks around here, so a deal on them is too good to pass up.
The program at Staples isn't instant-- that is, you don't get the rewards until your next statement, which can be a few weeks, depending on when you shopped. But if you roll your rewards into another reward, you'll still pay a small amount out-of-pocket and get more rewards back. I got this in my email and printed it out: