A Block Island destination is a great idea. You will want to say in the "New Harbor" a/k/a the Great Salt Pond. The holding ground is generally very good but leave plenty of scope because the wind can blow quite impressively each afternoon. Alternatively, consider picking up one of the hundred or so town moorings, which are about one nautical mile inside the harbor. The cost is $30 per night (at least it was during my last visit in 2000). You should have no problem finding an empty mooring from about noon on sunday through Wednesday. After that it gets a little tight.
Launch service ($2) is convenient and runs late. Free pumpout is very convenient.
Each morning Aldo''s bakery runs a floating danish/coffee/dessert service. It''s not bad - simply stand on your foredeck and waive or hail by radio oncy your hear the owner yelling something in Italian.
Old Harbor is small, busy, noisy (both from the ferry and the surrounding bars - if however you selected Block Island for its nightlife, you may wish to reconsider.)
Once anchored or moored make your way to Paynes dock and rent a bike - pass on the mopeds as they are an unnecessary expense and the locals hate them; moreover, the island is small and you''ll be cheating yourself by not seeing it by bike. Down town is no more than 1.5 miles from Great Salt Pond. An adaquate grocery store may be found there. You''ll have no problem biking groceries back to the harbor.
The ideal day is as follows - rise leisurely; bacon and eggs; loaf for a while; morning swim; loaf; ding ashore to your bikes (bring small cooler, water(lots), fruit, ects.); ride bikes through town along coastline to the Southeast Lighthouse (take pictures enjoy the view and sit on the big rock); return to bikes and continue down the road for about 100 yards until you come to a small parking lot on your left - you are now at Mohegian Bluffs; walk down the long wooden staircase and walk West for about one mile (the long walk is worth the effort because that you''ll be the only people there - even during the most crowded weekend); loaf for the day; return to the stairs which now have at least trippled in height; bike back to town but stop at the Atlantic Inn (large white hotel) for cocktails on the front lawn while lounging in Adirondack chairs; once duly lubricated bike to the harbor and dine at Dead Eye Dicks - it is located almost at Payne''s dock (get there early enough to grab a seat outside; eat and enjoy (don''t skip the Calamari - enjoy the sunset and hopefully a lonesome bagpiper); walk/bike/stagger to wherever you left the dinghy; make your way home for the evening and enjoy the dark harbor that is decorated by hundreds of anchor lights; finally, consider repeating the same sojurn, tomorrow.
While my wife and I love the island and its loafing opportunities, after four or five full days, you may have had your fill. The downtown is meager and the shopping opportunites (which for reasons that escape me seem to attract my wife) are essentially nonexistant.
It has often been said the Block Island is what Martha''s Vineyard was 50 years ago.