Not sure if you are traveling as adults or with children. Off the top of my head, here are some:
*Dry Tortuga's: Take the Fast Cat out to really get a good experience
*Hemingway's House
*Mallory Square for sunset celebration
*Restaurants: Blue Heaven for breakfast; Schooner's Warf happy hour appetizers and entertainment, Pepe's, Louie's Backyard (fine dining)
*Bars--long standing: Green Parrot, Sloppy Joes, Irish Kevin's, Schooner's Warf, Hog's Breath
Many of the above places in Key West have live feeds.
As you travel down through the keys.
*Key Largo: Key Largo Chocolate and Ice Cream. All home made ice cream, allergy friendly sorbettos, and chocolates. Factory on site and if during the week you can see the production through the windows. Rachel Ray voted their Key Lime Pie on a Stick the best frozen dessert in FL
*Tavernier: The Florida Keys Wild Bird Rehab Center allows you free up and close encounters with many of Florida wild life and great bay views
*Islamorada: Robbie's. If you have never been to feed the Tarpon a great quick stop. Even going on the pier and just observing is an experience.
Lorelei has good food and a great spot to catch the sun set depending on what time you are traveling through. Michael Trixx, puts on a fabulous magic show, is there M, W, F and starts just after sunset. He is known to draw a crowd.