Generally speaking, the coupon pictured or the coupon terms (small print) will indicate which items can be bought with the coupon. In the past some people have decoded the UPC code and managed to get discounts on other products that were not actually meant to be included in the promotion.
When is Decoding Okay?In many areas of retailing (such as clothing stores) decoding the UPC code to help determine what items are on promotion is okay. For example, a store might be running a promotion on all shorts made by a particular manufacturer and those shorts might be found throughout the department, many times without a sale sign or any other indication that they are on sale. By looking and matching up the UPC numbers on the item's price ticket, shoppers can determine if the item is part of the promotion.
But this same concept in not considered ethical couponing at the grocery and drug stores. The bottom-line in ethical couponing is to read the terms of the coupon and follow those terms. Use the coupon for the pictured or listed items only.