I keep my boat at Rodney Bay. Since the supplies are often limited or abundant, depending upon which container has arrived and been processed, I find it best to do all my shopping in person. There is a dinghy dock, as @Sunset_Sammy mentioned, close to the 2 Massys (the normal one and the "gourmet" one). Also, if you walk out of the marina there is another Massy about halfway between the marina and the Baywalk centre. I found that one to be well-stocked and somewhat cheaper, particularly when comparing it to the "Gourmet" store. A taxi ride price can be negotiated that is quite cheap. If you can, buy any beef before you go; prices and quality are high and low, respectively...