In Cabo San Lucas you have Medano Beach a quick water taxi will take you there. Also Cabo San Lucas has a place called The Glass Factory where before 2PM you can watch them blow glass.
The Glass Factory, Cabo San Lucas, Mexico
Mazatlan you have the cliff divers (they work on tips) a taxi can take you there. The Divers don't start until enough people have shown up. You take also take a water taxi to Stone Island. Or take the Pacifico brewery tour, this tour is free. Here is a link to the information.
Pacifico Brewery Tours
Puerto Vallarta I was looking at a day pass for the Dreams Resort. It's $45 for a cruiser day pass which is for 6 hours and (includes meals, drinks and beach towels). I have heard the Krystal resort no cost to get in but have to pay for food/beverages. You can also take a water taxi to Yelapa and depending on the time of year walk do to the water fall. In summer the water falls dry up. Yelapa is quite far from the dock about an hour or so each way. Under the side bar there is information on water taxis from PV to Yelapa.
Welcome to Yelapa, Jalisco, Mexico
I hope the helps give you some ideas.