You'll find these in the towns and cities of Crete - ad all over Greece, for that matter. What are they? Little street kiosks that are open very long hours.
They sell cigarettes, sweets, contraceptives, postcards, papers, drinks, komboli, toys, sandals, icecreams, books, batteries.. you get the general idea.
A cultural habit that is worth mentioning re the exchange of money:- when you hand over your money, place it on the little tray on the Periptero counter and your change will be placed there too. In the UK we hand money to shop and kiosk owners, but this isn't the done thing at the Periptero. I've noticed there are cultural differences in the way money and change is handled by shops round the world - email me if you've got any input on this from your own country!