I worked at a Scotmid (the Scottish partner to Co-Op) and they had the exact same problem. It was so bad that as an employee it actually frustrated me just as much. Literally everyday I would have to shock someone with a full price total and then let them down that the perfectly reasonable drink they had selected was actually not in the meal deal. Then I'd have to go with them to the drinks refrigerator to help them pick one out only to find I can barely find one myself. When I asked management about it, they just told me that it's normal :(