Best things to do in Athens - walk around and look at all the beautiful buildings (not only the ancient) and go to Cine Thisio, an Open Air Cinema that´s amazing, one of the best I´ve been to. 

Best food - Atlantikos, a small fish restaurant that doesn´t look like much, but so good genuine greek food and the best staff. Avocado had a real good veggie burger, probably the only all vegetarian restaurant in Athens..