As superyachts and megayachts bottle up Nantucket Harbor, it’s a sure sign the millionaires and billionaires who frequent the island are headed ashore for shopping, dining, and a respite from boating (and the occasional legal battle). There’s something on the island for anyone with too much money to count, from the nuclear shelter built for President Kennedy to a private golf club frequented by Bill Gates and Warren Buffett. Here is where the wealthiest regulars stay and play on Nantucket.