well, costambar isn't much
the supermarket sells about everything plus some gringo stuff. they are open all sorts of hours and they will deliver if needed. there is a prarmacy in case of stomach or erection problems
close to the beach there is also a small colmado, your best shot at getting things late or on weekends.
we have a library attatched to the APC office.
few restaurants mentioned above.
as far as annac question: costambar is very close to POP. if needed one can walk (about an hour to the city centre). 5-15 minutes by car, depends on the traffic and your driving style
just outside the gate you can get a carrito publico that takes you to the city, about 30 pesos now, i would say. you can also walk all the way to the main road and take a larger guagua, 25 pesos. a motor from the city should be about 100 pesos.
main street is nicely fixed. there is an emergency unit there in case you need it. opposite the emergency, in the shade, there are food stalls: fresh fruits and coconuts.