Playa Lancheros is a great open air Palapa Restaurant and beach area to visit and enjoy. The restaurant caters to a mix of locals and tourists.
We missed the day-trippers from Cancun, but I understand they make frequent stops here.
The specialty is the tic n xix (spelling??), a kind of Mayan spicy/bbq fish dish that is grilled on a large open grille near the dining Palapa. It is served with a salad, rice and beans, and a single order for $5 - $6 was enough for two - very good. We also had grande bottles of Montejo cerveza - muy barato (cheap).
The day we stopped in for a late lunch there were a couple of friendly musicians playing traditional mexican tunes on their guitars. It was a great addition to the already enjoyable atmosphere.
There is a beach stretching out in front of the palapa, so you could turn this into an all day beach and dining day if you wanted.
Playa Lancheros is located on the west coast of the island, you pass it on the main west side road heading to the south end of the island from donwtown. It's a short taxi or cart ride from downtown.