I just realized that there was another coupon for Arby's...FREE Market Fresh Grilled Chicken & Pecan Salad when you purchase a Pepsi Beverage. (found here)
If you use the coupon for FREE Roast Beef Sandwich and the FREE Market Fresh Sandwich, you could have a really cheap lunch date. Buy a Pepsi to share and get both sandwiches for FREE...probably around $2.00 for lunch for two.
(Note, the coupon does state not valid with any other coupon or offer, so you'd have to order separately.)