So a few weeks back, I was in this situation. Since I'm addicted to my iPhone, I decided to just look up my rewards on Safari. It's easy - go to www.Staplesrewards.com.
After you log in, you can keep it so your phone knows you. Now, whenever I go to Staples, I don't even print out my rewards - I just pull them up on my phone for the cashier to scan. See:
Isn't that cool? What's even cooler is that because of this blog post, I learned how to take a screen shot on my iPhone. Simple things amuse me. Save paper, save time, use your iPhone!