The beach is all you need for the Florida experience. Go out on the pier and watch dolphins ($2/person for a whole day), go kayaking or paddle boarding off the beach ($20/30 minutes, well worth it). Hit the beach at night to catch all the crabs out (be sure to bring a flashlight and bucket). Be sure to visit a surf shop.
Okaloosa Island beaches are quieter than Destin, if you want a party, Destin beaches are where you'll want to go.
Parasailing is well worth the money, usually between $70-$80/person.
Hit up Fuddpukkers in Destin - it's a whole experience, not just dinner - they have an alligator experience, arcade, live bands, shopping, and more all in the restaurant. Wait is usually an hour or two but with everything to do it feels quick - we didn't get to do all we wanted before our table was ready and had an hr and 30 min wait. The Back Porch is Destin has great food & beachside deck seating.
Have fun! FWB/Destin is a beautiful place!