In Greece, the land is very rocky. Where land is flat, the soil is no good for farming.
Due to this reason, the Greeks became traders. They traded all over the Aegean Sea, and a little bit beyond.
Their diet consisted of seafood, because fish was plentiful in the Aegean sea. It also included olives, which was a gift from Athena, barley, wheat, and a beverage made by Dionysis: wine. The Greeks also kept lots of livestock, mostly sheep.

The first 'Greeks' were the Minaons, closely followed by the Mycenaeans. The Minaons lived on Crete, but were more or less wiped out by a volcano on their island.
Mycenaeans, on the other hand, lived on the mainland, and, like later Greeks, were great traders. When the Minaons were wiped out, Mycenaeans noticed first, bacause of their vast supply of ships, and they took over Crete.

Greece has hundreds of islands. They are spread throughout the Ioanian, Aegean and Mediterranean seas. The Greeks were great sailors, and they had no trouble navigating their waters to find their islands.