Kayak the mangroves on the top of the island. Go snorkeling. Take a 1/2 day fishing charter. Wade the shallow water of Smathers beach. Go to Irish Kevin's bar on Duvall St. Take the wife to the dessert restaurant "better than sex" (it's not, but damn close). Eat breakfast at the Blue Heaven. People watch on Duvall Street at night.
Hehehehehe.
People watching can be a full time thing there. I still have family living in Key West. Interesting place.