There are two obvious observations to be made about food and drink:
Nothing beats a spontaneous drinks
party on a neighbour's boat
The difference in price between supermarkets and small shops can easily be double. For instance, in Spain large supermarkets offer drinkable wines for under 2 euros, whereas it is difficult to get anything except paint stripper for under 4 euros in local shops. To be even more specific, Eroski in Spain have an adequate cava for 1.50 euros, and I have never seen a cava for under 5 euros in a local shop.
Produce markets are variable. In some places, they have become expensive tourist attractions; in others, mainly in larger towns with little tourist appeal, like Fuengirola in Andalucía, they compete with supermarkets on price and win on freshness and variety.
Cheaper supermarkets and produce markets are often inconveniently far from available berths and landing places. So, you really need a bike to get to them and carry a heavy load back. And the bike either needs panniers or a trailer.
|Invitation to a local's wine cellar in Sardinia|
As for avoiding restaurants without feeling hard done by, I think the secret is to be anchored in a beautiful bay. Come the evening, when you consider whether you would like to visit a restaurant, you reflect that you are enjoying a magnificent view, whereas the restaurant with the best affordable food is in a back-street or basement, that you can have a swim between courses, and that it would be a fag going ashore anyway.
Restaurants are better value at lunchtime and, especially in Italy, you need to visit a few to discover how delicious pasta with the simplest of sauces can be. Then you can cook something similar aboard!