There are a number, which mean’s I can’t remember how many exactly. You can certainly buy many general purpose items including basic medicine: Aspirin, seasickness tablets etc. Other shops sell jewellery/watches, camera's, "Cunard" sweatshirts etc. Shops onboard ships are rarely very cheap, yet not all items are overpriced either. The book shop is the best afloat for maritime books. Book signings sometimes take place (Bill Miller, John Maxtone-Graham etc.).
Many thanks for your prompt and most helpful reply.
There is of course a medical centre with Doc and Nurse, although there are fees.
(If you are worried about seasickness, there a wonderful magic "jab" you can have).
I've heard that there is an excellent medical centre on board, but hadn't heard about the magic "jab" for seasickness - that is really useful to know. Many thanks.