This post is a little off the beaten path - it's more a savvy-consumer post. I generally take my insulated travel coffee mug with me, because I'm a tree hugger and I don't care to waste the paper cup (also, being insulated, it keeps my coffee warm longer). Interestingly, however, about 30% of the time I am given a significant discount (Starbucks sometimes just charges me 50 cents). Today, in fact, I wasn't charged at all; the server just said, "Nevermind, free refills." I'm not angling for the discount--I'm happy to pay for my coffee--but if it's offered, why not?
I think I've probably unintentionally saved at least $20 over the last six months just by having my travel mug with me. Try it yourself. Even if you're a paper-wasting environment hater, it might just save you a few bucks.