Supermercado Morales is the largest grocery store on Vieques island and offers many items that you see in a small town market such as peanut butter, chips, bread, milk and the basics.
One important note of interest is that fresh vegetables and dairy products come over from Puerto Rico early in the morning on Wednesdays so you will have a good selection beginning on Wednesday and waning toward the weekend.
You can also purchase beer, wine and liquor as well as sodas and water by the bottle.
Another point of interest is that there are two Morales Supermercados and you can see this is the larger one of the two with the easiest access and parking. See the map for the central location of Road 200.