conch fritters? frozen key lime pie is pretty effin awesome. spent very little time there. Stopped off on a cruise.
Went to Key West a few years back when we were staying in South Beach for a few days. It was tourist-y, but we still went tto Hemingway's house, SLoppy Joe's bar (Hemingway's hangout), etc. We also went and watched the sunset and performers at Mallory Square. It was actually pretty entertaining. All of it was a "so I can say I've done it" deal, but worth it.
Diving in the National Park if you are SCUBA certified. Best fishing is probably out of Key Largo. Do spend some time on the other keys - don't just drive through to Key West and think you have seen it all. Great kayaking, and kayak fishing in the backwater swamps. And hit South Beach on the way down - a different kind of scenery, but plenty entertaining!
The best key lime pie in the world is at Tower Pizza, Mile Marker 100, on the north end of Key Largo. I know. I'm an expert. Pizza, calzones, all good. Key lime pie, amazing. In Key West, go for the Blonde Giraffe key lime pie.