Ha! I only wish I was staying a month! We're staying a week.

There is a brand new Chedraui supermarket there now, as well as smaller grocery stores, from what I have heard Chedraui is about the size of a Walmart.

Most of the better snorkeling is from a boat, but there is snorkeling by the bridge at the Avalon as well as at Garrafon de Castillo, admission $5, they rent gear, have a snack bar, lockers and clean restrooms. Right next door to the pricey Garrafon Beach Club.

Drink bottled water, it is sold everywhere, street vendors are fine also (be sure and get a Bimbo hotdog, SO good) as well as the marquesitas (kind of like a crepe thingy).

Our last night there we would always eat at Villa Rolandi hotel, it is expensive but if you do not order apps, salads, deserts, and just stick to one main course and maybe dessert you can make out OK, around $100-$120 for two with tip.

Buy a Mapchick map, cancunmap.com, like a mini guidebook.

Lots of good questions, I'll try and answer a couple.

I completely disagree with the advice to not eat street vendor food. Please, please do try the street vendor food. It is some of the best and most authentic you will have. It is very fresh and safe to eat, I'd say a LOT safer than the stuff at AI's that sits on a steam table all day. As for the water, it's probably ok too but I do stick with bottled water partly because the best preventative for lots of issues is staying well hydrated.

As for beach days, there are many beach clubs that provide chairs and umbrellas. There is a nominal charge and you are expected to purchase food/beverage from them, no carry in's. If you do not want to do this route and bring all your own stuff, unless you like laying on the sand with no shade you'd need chairs and umbrella. Many condo's provide those with the rental so check that. I spend very little time in the direct sun. It'll burn the hide right off of you if you're not very careful.

As for appropriate dress, spaghetti strap tops (and some a LOT smaller) are perfectly fine and quite common. Even topless bathing is fairly normal although I think I see less of it lately than I did 10 years ago, just don't be surprised.

Have a blast, a month is a nice long vacation!

We rent out our condo in Playa del Carmen, and know some friends who rent a place out in Isla Mujeres also. Our place in PDC (and every other house and condo rented by our management co, Latido de Mexico) and our friend's place on Isla Mujeres come with a large 5 gallon plastic bottle of purifed water, and a dispenser for it. And the purified water is replenished as it runs out during your stay. That is part of the rental fee. I would inquire as to whether that is the case in your rental. It really should be, esp. considering it is a house.

You will need LOTS of bottled purifed water over course of a wk., for making coffee, brushing teeth, soaking all vegetables and fruits (tomaotes, mushrooms, lettuce, apples, etc.) in microdyne disinfectant if they do not have peelable skins. And of course drinking water to make iced tea or powdered drinks out of, or just to drink as is, take to the beach, etc. I's be surprised if your rental doesn't include the 5 gal. plastic jug water.

As for what else to take w/you to the beach, TAKE A HAT!!!! A wide brimmed straw hat for walking on beach and sitting in beach chair, and we also take a visor we can wear while bobbing around in the water. Sun is intense, even this time of yr.

We provide a good Tommy Bahama beach umbrella w/screw at bottom of pole for our tenants. And 3 foldable backpack chairs that can be put on your back to walk to beach (our condo is only 1 blk from the beach, but we want to give renters the option of not having to pay for beach clubs and to be able to just go to the beach our equipment).

We also provide a soft rolling coller that rolls nicely onto the sand. So check w/your owners and see what they provide.