Groceries:

Where you go for groceries depends on how much you want to cook. Martin's in town has all the essentials you will need for breakfast and lunch including bread, fruit, milk breakfast cereal and beer, etc. It's bigger than your typical 7-11. You will also find individual vendors selling pastries and fruit around town.

If you want to stock up or want more variety there are major grocery stores in Playa or Cancun. Commercial Mexicana in Cancun is easy if you are taking the bus. as it is right across the street from the downtown bus station. If you are driving you can try Chedraui which is on the beachside of the main highway at the far end of Playa del Carmen. Chedraui is also in Cancun on Tulum street (also the main highway).

There are three Wal-Marts in Cancun. To get to the one I know of turn left on Coba and left on  Labna. Sam's Club is right there too.  Costco is on Kabah. There is a Sam's club in Playa right on the highway. 

Liquor:

Beer, wine and hard liquor are available at Martin's in town. If you are shopping for something special or want better prices try "La Europea" in Cancun. It is located in the Plaza Hollywood across the street north of WalMart. As you face WalMart it is to the right. They have a huge wine selection and the best liquor selection that I have found so far. Most of the major grocery stores have good prices but only a moderate selection. Wal-Mart and Costco have good prices also, but less of a selection. If you want to bring something back, the duty free stores have very good prices. Selection has improved with the new terminal building. If you buy at the duty free, you will need a non-stop flight to bring it back in your carry on luggage. You can now carry your purchases directly onto the plane from duty free. If you have a connecting flight you will need to find room in your checked luggage for liquor. The limit on liquor I am told is two liters per person. I haven't had any trouble bringing back a little more, but that is your decision.

There are deposits on some beer bottles. I am told it is primarily on the long neck bottles. I haven't figured this one out yet.

If you want to learn about fine Tequila try this link:  http://www.tequilasource.com/

Starbucks:

There are several Starbucks in Cancun now. I don't go there much. There is one in the same Plaza as the liquor store above across from Wal-Mart.

Playa Del Carmen

It’s great for shopping. You can take a taxi or the collectivo out to the highway. Cross the highway and go a few businesses south to the bus stop building. You can buy your ticket there for under $2. The buses are clean, comfortable, air conditioned and show movies. The bus will take you to the Playa del Carmen bus station which is right downtown.  5^th ave is the main shopping street and it runs parallel to the beach about one block inland. There is a Sams Club and a huge supermarket (Chedraui) on the highway

Cancun

It’s an easy bus ride from the highway too. You can take a taxi out to the East side of the highway for about $2 and buy your ticket at the bus ticket stand. The bus costs less than $2 per person and goes directly to the Cancun bus station. The Cancun bus station is right across from Commercial Mexicana which is a big grocery store. You can take a city bus or a taxi within Cancun or out to the Hotel Zone. Cancun has everything including Costco, Wal-Mart, Sam's Club, Soriana, Chedraui and Commercial Mexicana.

Craft shopping:

Market 28 is a nice stop. They have the tourist type items, but the prices appear to be more reasonable. You see a lot more locals shopping there. There are several inexpensive restaurants there too. It is located a little north of WalMart. Take Coba and turn right on Tankah. There is a small US style mall there too- Plaza Bonita. Another craft market is Ki-Huic which is on Tulum.

Mall Shopping:

You would have trouble missing Plaza Las Americas along Tulum. It is a full sized mall with a food court and all that.