You may already be familiar with Office Max's incentive program MaxPerks. If not, it's basically a card you swipe with every purchase and you receive 5% back to spend on more office supplies. (The shopping list is always endless, right?) Occasionally, they will offer up to 25% back on certain brands or items. If this isn't worth it, the valuable coupons they send out definitely seal the deal.
Also, I found out the other day that for every empty ink or toner cartridge you turn in at the store, they put a $3 credit on your reward balance. You can turn in up to ten cartridges a week. This can really add up over time - especially if you have access to some cartridges from the office or elsewhere that are getting thrown away anyway.