I am not a professional but as a customer I will let you in in what gets me to come back to the same pharmacy each time. I don't think merchandise will help a pharmaceutical business but I do think that anything regarding to service will get people coming. The time you wait in line, the way the pharmacists talks to you, if he has a smile on his face , the  way the products are organized on the shelves if the prices are clear and visible . How easy it is to find stuff . You might want to invest a bit in he bags you hand out to the costumers maybe advertise on them some special offers or something.