Though not usually prone to particularly ´touristy´ activities, this boat cruise was great (boat was called Dancer). For only $20, you are given breakfast on the boat and a cooked lunch at a restaurant. It is something of a party on the boat and full of other Mexican tourists.
The first stop is at Los Arcos, huge rocks jutting out into the sea. Here you can jump off the boat and snorkel (everything is provided). Snorkeling is good, with lots of fish, stingrays etc. After Los Arcos, it is Las Animas, a beautiful beach, even though it can get a little crowded from the many boat tours there (however, you can get a water taxi from Boca de Tomatlan or Playa de los Muertos and stay until the crowds have gone). Quimixto, although it only has a small rocky beach, does have a fun waterfall where the locals cliff dive.