First, the good news - most people in Playa speak English. However, it certainly won't hurt to know some Spanish. Not only will it will help you get around, it will reinforce the good feeling that you are no longer at home ... you are in an exotic locale!

Learn the basics here...

The Bare Essentials

There are a few words everyone should learn, as you'll speak and hear them everywhere you go:

Buenas dias! - "Good day!" (before noon)
Buenas tardes! - "Good afternoon!" (noon - 8pm)
Buenas noches! - "Good evening!" (after 8pm)
Hola! - "Hello!"
Adios! - "Goodbye!" (in other parts of the Spanish-speaking world, adios is typically not used as an everyday goodbye, but in Playa it's ok!)
Por Favor - "Please". You must absolutely know this word, it is quite rude not to use it when asking for things.
Gracias - "Thanks"
Muchas gracias - "thank you very much!"

Getting Around

Playa is a small town, so this isn't as much of a problem as it could be elsewhere. No cabbies to deal with, a few main streets ... it's all quite easy. But a few words will be helpful:

Calle - street
Avenida - avenue. In Playa, most of the action happens on 5th avenida, about a (US) block from the seashore.
Alli - "there"
Alla - "over there"

Shopping

The local shops are an exception to the general rule that everyone speaks English. Many employees are native Mexicans and not all have a good grasp of English. Fortunately, you'll need only a bit of vocabularly to make it through.

La Cuenta - the bill. A good way to ask for your bill (and will definitely get you faster service than patiently waiting for the server to bring you the check) is to say, "Amigo! La cuenta, por favor!" (friend! the check, please!)

Tiene...? - "do you have ... ?" This can be a bit tricky for non-Spanish speakers because you probably won't know the word for what you want. However, it helps to get the idea across that you are asking for something. For example, "Tiene los libros de viaje?" means, "do you have books about travel?".

Necesito... - "I need...". For instance, "Necesito unos cigars, por favor!" will get you a selection of stogies to choose from (or directions to a local cigar shop).

Quiero - "I'd like..." or "I want...". "Quiero unas camisas, por favor" means, "I'd like some shirts, please".

You may want to ask how much something is (understanding the answer is another matter). To do so, ask "A como son estos?" (How much are these?)

Haggling

Don't want to pay full price? Here's where a basic understanding of Spanish really pays off. Most tourists will pay the asking price for the goods they buy, but this is certainly not obligatory. Offer the shop assistant less, starting at perhaps half price. This requires little more than knowledge of how to count in Spanish (if you try this in English, many shop workers will pretend not to understand in the hopes that you'll give up). It may seem strange to Americans, but it will help your cause (and is expected) to get a bit rude and impatient with the shop keeper. You should certainly threaten to walk away and shop elsewhere. Sometimes you'll just save a few bucks, but on higher priced items, you can save a lot more!

Some shops will not haggle with you. These are usually the expensive looking stores run by expatriate Americans. In any case, there will be signs prominently displayed in English informing you of this. It doesn't hurt to ask, but in these shops the employees probably do not have the authority to sell at lower prices.

Nightlife

Again, if you know no Spanish, it is probably best to stick to the tourist bars on 5th Avenida. However, if you can speak even a little, you'll be perfectly fine wandering off the beaten path and going to some of the more local hangouts.

Words you might find helpful:

El trago - "shot". Of course, you'll probably not be ordering just one, so you'll want to say "unos tragos" (some shots). For example, "Quiero cuatro tragos de tequila, por favor" (I'd like four shots of Tequila, please).

Cervesa - "beer", as in "Dos cervesas, por favor" (two beers, please). If you aren't specific, you'll end up with the house beer, either Sun or Corona (both quite acceptable). Budweiser and Miller products are less common, but can be found in some bars.

"Margarita" and "Daiquiri" are the same in English. And don't worry, gentlemen, it's perfectly fine to enjoy a frozen drink on a hot day, although after sundown you'll fit in better by sticking to beer, mixed drinks, or shots.