Can you visit the Caribbeans "on the road"? Yes you can, we choose some of the Widnward islands to do this. Arriving in St George, Grenada, we made all the way up to Kingstown, in St Vincent, hopping from island to island with local boats.
You don't need much preparation, just be ready to ask a lot locally when the ferries / cargo boats are departing and be there on time with a lot of patience. On the islands, especially the biggest island, the transportation system is pretty integrated: catch one of those crazy minibus and go on your feet to complement the are where vans are less frequent.
GRENADA: we started in the capital of St George. A nice colonial cities in the Antilles. However, don't expect the beautiful colonial buildings of Old Havana, here the colonization was led by the French and Brits with their more spartan and essential architecture. The crazy but funny minivan transport system allows you to reach every spot of the island in less than 90 minutes. We randomly reached the north east of Grenada and stopped by to a Cacao plantation and a Rum distillery. Grenada also have nice beaches. The Grand Anse is the main touristic spot of the island with Turquoise water and fine sand. Not to crowded tough.
CARRIACOU: 3 hours away from Grenada, on the North, there is the sleepy island of Carriacou. The place is magic to slow down and stroll around with no stress. There is a small expat community (mostly British and Americans) who retired there and are meeting at the cafe near the pier. Nice for a chat. The small town of Hillsborough has a couple of restaurants to feed you but don't expect much nightlife.
UNION ISLAND: this island is an outpost and the Southernmost point of St Vincent and the Grenadines. Rough, with many sailors, not nice on his own but with a strong feeling to be in a transit port where different people cross. Getting here from Carriacou takes almost a full day, of which 45 minutes spent on a small cargo boat and 8 hours spend doing border crossing bureaucracy and waiting.
TOBAGO CAYS: unless you are sailing with your own boat, the only way to visit these small islands (where they shoot the Pirate of the Caribbean) is by a boat tour from Union Island. Great snorkeling and a day out.
BEQUIA. The best island in our view, just an 1h of ferry from St Vincent. Relaxed, chilled out, pure Caribbean life. Good mix of remoteness and leisure with nice beaches, wonderful hike trails and good choice of restaurants. History is interesting tough as these island where not colonized until late 18th century and were the only independent Carib country for a while. African slaves escaped from nearby colonies also sought refugee here. Unfortunately in 1796, after having fought against the Brits, part of the Carib population was deported to Central America and are now known as the Garifuna people.
KINGSTOWN: the capital of St Vincent is as described in every guide. Uninspiring, but its street beat raeggetton in the evening and is not a waste of time stopping over.
PORT OF SPAIN: a metropolitan city (relative to the Caribbeans), the capital of Trinidad and Tobago probably offers more to business men than travelers.