One option that many food outlets use is the custom-printed stadium cup or travel mug. Order a quantity with you name, logo, phone-in order number and address. Offer free refills of soda, coffee, or tea with any sandwich or meal purchase. You can even put a terminal date on to limit the refills to one year or now through December 2009, etc.
Another option is with the travel mugs, offer 99 cent coffee or $1.79 (or other price discounted from your regular price) when they bring in your mug for refills. Set the price high enough to make a profit, knowing you won`t be providing them a styrofoam or insulated paper cup. The every day discount will have the same appeal as a coupon (instant savings), but without the distribution cost of repeat newspaper ads or mailings.
You might also offer a punch card, where the holder gets one punch with every $3 or $5 purchase. Once the card is filled, they get a free travel mug, cap, or tote bag. Any item you give should have your name, logo, and additional info to invite additional customers.
Just a couple ideas that might help build repeat traffic. It can cost you 5 to 9 times as much money to bring in a new customer as it does to retain an existing one.
Good luck with growing your business.