The St. Pete Pier and the surrounding area on Beach Drive is full of great restaurants, bars, boutiques, and just a nice place to walk around. Also, check out some of the museums nearby (Salvador Dali, Imagine, etc.)
We might be bias (But honestly, I don't think so). We have some of the most stunning beaches- you can't go wrong with any of the beaches along Gulf Blvd! Some of our favorites are St. Pete Beach, Pass-A-Grille Beach, Upham Beach, Madeira Beach, and Indian Rocks.
An absolutely stunning state park. You can walk, bike, run, or even rent kayaks.
If you get sick of the beach for some reason and want to go explore Tampa, the Riverwalk is a great way to do so. There is even a ferry that leaves from Downtown St. Pete that will take you over there! Make sure to say hi to UTampa (where we went to college) while you're there.
Tons of breweries, boutiques, restaurants, etc.