A good place to buy things to take with you on the ferries to eat and drink during the trip or while travelling about your destinations. Especially stuff like big bottles of diet coke, sunscreen and body lotion, fruit...
at a much cheaper price than buying drinks at cafes or shops along the way.
This is a great little covered locals market with its stalls of fresh fish, meat, charcuterie and fruit and veg as well as a couple of smaller shops specialising in cheese and olive oils. Just having a quick nose (literally) even though I had no intention of buying anything made for a pleasant little detour and a glimpse of local life as the shoppers prodded, smelt and bartered with the stallholders.
What to buy: Fish is obviously the main thing, fresh from the local boats.
What to pay: Whatever.