Kids walk up and down the beach trying to sell things to tourists. They sell books often, or wax for waxing surfboards. They don't really want to just sell you a book, they want to trade 2 or more of your books for 1 of theirs, or trade 1 for 1 plus money. In any transaction they want their library to either remain unchanged in size, or to increase. They enjoy the trading probably more than the money.
Fishermen walk along the beach selling their fish.
It will feed 6 people. You buy it from the guy, then you get the house to cook it for you. They take care of all the side orders, like rice. All in all it's a very inexpensive and convenient system. Anyway I met Axel at one of these lossmen.