Myakka basically has fishing, hiking (if you can call walking through a perfectly flat landscape "hiking"), etc. For freshwater fishing I prefer Lake Manatee, which has less annoying bugs and less people.
Try Anna Maria Oyster Bar (more of a restaraunt than a bar) on 41 a mile or two north of the airport. Everything there is good. A lot of the restaraunts here are less expensive than you would expect because of the "old people effect".
The best fruit market I know of is on Prospect near Whitfield (small market and very cheap). Lots of citrus is in season right now.
There aren't any real views of the ocean - everything is flat. Some of the beaches here have kind of crappy sand because they've been pumping it in to compensate for erosion. That pumped-in sand just doesn't have the quality of wave-scrubbed sand. My favorite beach is Manasota, mainly because it has the most petrified sharks teeth. It's a bit of drive from Bradenton Beach though.
The aquarium on Lido key is not bad.
The water temps are a bit above normal right now, but still around 70 degrees. To me, that is "quick swim and get out" temperature (and only if it's a warm day), not snorkeling temperature.