I second loading up at Bobbys via their online form, it will be delivered to the dock when you arrive as well. There is also a grocery store in Road town just a 5 minutes walk from the Moorings base along the road. (Take a right outside of the gates and head past the Ark Vintage store, you'll see it across the street past the Gas station)
There is another great grocery store in Soper's Hole. Make sure to head upstairs for the Lavish European food goods including a full service deli. There is another grocery store on Tortola itself in west end, you can dock there and step off quickly. They also have an ATM which you will no doubt need for Mooring fees and additional booze funds. Theres a fruit market there as well in season which makes for fresh nice rum drinks.
Don't forget the floating grocerystore on Norman Island. You can call in your request via radio or step off near the Pirates Bight and ask there.