OK: optionals on Greek cruise:
they give you a long list and David, our TG, went thru what he recommended.
In Mykonos, you must pay (I think) 4 euro each for a shuttle to take you back and forth to town from the boat. But it runs all day long, and you can go back and forth: I went back in at night to wander around and it was lovely, quieter and all lit up. Probably my favorite island.
in Patmos, many people went to the St John's Monastary and Grooto: we didn't, but I heard good things. It was 49 Euro pp.
We did Ancient Ephesus in Kusadasi: HIGHLY RECOMMEND! 57 Euro
Also did Thira and Oia Village in Santorini: also highly recommend, it was wonderful and a great way to see the Island. That's where I rode the donkey down, but you can walk, or take a quick cable car. 53 Euro.
In Istanbul, we did an optional with Omer to the Spice Market and a cruise on the Bospherus, as well as the Beylerbeyi palace. very nice, forget the price, though!
In athens, we did a day tour with Chat tours (insight rep booked us.. pretty much the only thing she did for us there!) to Delphi with included lunch: really nice. it was pricey, but worth it. 96 Euro.
Are you staying an extra day in Athens?

Thanks Brooklyn - really useful to know all that. We are going to Ephesus on the Turkish Delights tour commencing 24 Sept (this week!). I think I would like to do the Patmos optional and Santorini. The tour of the Bosphorus is included (I think) in the first tour we are doing. We are not staying an extra day in Athens but plan to check out some local interests on our day there.