comfortable walking shoes and sandals for greece

I used clarks wave whisk sandal, loved them. Unfortunately, they have been discontinued but they were wonderful. I can't speak for Santorini or Mykonos specifically but the one thing I wish I would have remembered was the water shoes. Some of the beaches were very stony. My husband did wear his & he did much better.

Mary

We were in Athens and Santorini in October about 2 years ago. It was not as warm or as dry as you might expect. I wore my Ahnu Montara boots with Sockwell compression socks for all daytime walking, museum visiting and hiking. I will call going to the Acropolis a form of hiking.

I usually switched to regular comfortable flats for walking to dinner, depending on the weather. I wore these Ahnu flats for that, but today I'd wear these Abeos.

The beaches on Santorini are not on the same side as the caldera/scenic side where most people stay. It's quite a walk over the hill, to and back from them, if you stay on the caldera side. There is a bus that you might be able to take. I'm not a beach person, but I'd guess the water will not be very warm.

In general, the islands start to slow down in October with the cooler and wetter weather and rougher seas. A lot will depend on when you are there.

I don't know what you mean by a "suitcase." Pack light and use a roller bag or backpack. We flew from Athens to Santorini and used fast ferries for all other island transportation. Arrival on Santorini was pretty dramatic for that Aegean plane. The wind and water was so rough that the Flying Cats and Sea Jets couldn't go as fast as they can when the seas are calmer.

And if you haven't been to Greece before, be aware that you typically don't flush used toilet paper down the toilet. You put it in a trash can next to the toilet.

My mom & I visited Athens, Santorini & MyKonos in early October (2008)

I like my Keen Rose sandals & they are my go to sandal when I travel.

I didn't go to the beach while in Santorini, however, we did enjoy Ornos beach in Mykonos.
I actually went in for a swim while my mom took a nice nap (she was supposed to be watching my backpack with my valuables!) on a lounge chair under the shade of an umbrella.
The Aegean Sea is high in iodine & it was so refreshing to go in the water. You don't need shoes at this beach though.
We pretty much had the beach to ourselves, as there were only 2-3 other people in the water!

Enjoy your trip!

Oops! I forgot to address your other question.

We travel with a small carry-on size roller suitcase ( 22", counting wheels & pull handle) each.
We actually left one of our suitcases in the hotel in Piraeus & only took one of our suitcases on the ferry ship.

If you take one of the large ferry ships, such as Blue Star, you leave your suitcase on the steel racks on the sides of the ship as you board the ship, via the car ramp. You then go upstairs to your seat. Make sure you take all your valuables with you.
When you arrive to your destination, it's a bit chaotic because everyone lines up on the stairwell & everyone wants to get to their suitcases (which may end up all piled on top of each other). So, it's key to travel light!

In terms of taking domestic flights in Greece or Europe, make sure you read each airlines' baggage limits & sizes.

Enjoy!

I confess to using nice thick New Balance tennis shoes some days and for climbing ruins. On different trips I have used Wolkys (wonderfully lightweight), Keens and Chacos ( which I used on the beach as well; yes- water shoes are useful, especially if you can wear them when dry) Keens fit my high arch right off the shelf without breaking in. Merrells are also good shoes if they fit you.Mainly, try them on and wear them before packing them.
You can have sandals made for oyu whilein Greece, but they seem to be very flat leather- no arch support!
I am a roller bag user- 4 wheels are nice for smooth terrain and can still be carried.