Here's what happens if you purchase things in some stores in Brazil. I like to call it the 5 Card Monty. You'll find that it happens in places like hardware stores, pharmacies, and small grocery stores.
I will give you a true example of what you might go through trying to purchase a bottle of water on the way to the beach.
First you look around till you find what you want. Invariably you will find it behind the counter, as there is very little left out in the open. Once found you point to it (assuming you don't speak Portuguese and can just ask for it). The individual behind the counter will smile at you quite a bit, and hopefully identify the proper item. This person will fill out four (4) slips.
He will keep one of these slips, hand you two, and will hand off the fourth to someone else. The first time this happens to you will say, "What the hell do you want me to do with this. I just want a litre of water you moron"
At this point the counter person will point you towards the cashier. You can then go to the cashier, and pay for the item. She will then take one of the slips for herself, the other she will stamp paid, and hand it back to you. At which point, if this is your first time, you will say "Holy crap, now what!" At which point the cashier will look at you with a look of surprise, mingled with fear; and point you towards a third person, who has kindly wrapped up your purchase in a cheap plastic bag.
After reviewing your slip he will do some stapling with some other slips. He will then hand you the item, along with your stamped "paid" receipt. As you leave the store someone will examine your purchase and your paperwork. At which point you go outside and scream "YOU PEOPLE ARE ALL COMPLETELY NUTZ YOU KNOW THAT!!"
The best advice that I can give you in this matter is to not purchase anything on the way to the beach. There is simply no need. Everything you could possibly need is available on the beach. And I mean everything.
The first time we went to the beach in Brazil, we found a kindly older man, who was willing to rent us some chairs to sit on. In Brazil this is kind of an agreement. The person that rents you the chair will now try to provide you with your every need and want. He will come and offer you cokes, Ice cream, sandwiches.
After we had been on the beach for a while, soaking up the wonderful scenery, our vendor came up to my co-worker and I, and started asking us questions in that lovely Portuguese language, that we understood not a word of.
After a few shrugs and a shaking of the head, our vendor went off in search of an interpreter. He came back with a gentleman of about our age. A brief conversation between them ensued, after which the interpreter turned to us.
"He would like to know if you gentleman desire that he bring you some women."
"No! No! Thank you anyways." As we broke into fits of laughter.
Our vendor then added some more, to which our translator turned to us again: "Maybe some little boys?"
"HEY! NO! Cripes, we're fine with the cokes thank you very much"
Our vendor looked at us very strangely after that.
Needles to say anything you might need can be gotten at the beach. So avoid the 5 Card Monty.