Right on Playa los Muertes / Zona Romantica / are some nice restaurants. If you buy food and-or drinks you are welcome to use their beach, bathroom etc. populair are la Palapa, Langustines, Dairy Dick and more.
You need a cab to get there. White cabs in port charge more as they have to pay porttax. They often chrage per passenger.
Yellowcabs from the highway are cheaper and will charge around pesos 60.- per ride.
In all cases check the rate before riding a cab.
Or take the citybus from the hightway ° destination Centro/ and walk for a few minutes. Back a bus to Walmart/Sams´s which is opposite the cruise terminal. Bus costs 5.50 pesos per person per ride.