Greece packing tips needed

I was really happy with how a pair of PrAna 97% nylon slacks worked for me in both cool weather (with a pair of long johns on cold/wet days) and on hot days (up to about 90F). My other preference for slacks is something that's all-cotton or cotton with just a tiny bit of a stretchy fiber. Rayon/modal is also good.

I mostly use 100% cotton tops because they're so easy to find online or at Macy's, but I'm sure there are other decent options. You don't want polyester. For me, 3/4-length sleeves and long sleeves aren't any hotter than sleeveless tops. Wearing sleeves keeps my dermatologist happy and really reduces the amount of sunscreen I need to use.

Take a broad-brimmed hat. Important: The sun's reflection off water can be fierce. I once got badly burned while sitting on a bench, not in a swimsuit, somewhere on the coast of Greece. Protect your face (even if you're wearing a hat), ankles, etc. Also the top of your feet if you wear sandals.

It can be rather cool along the water after the sun goes down in May, and a breeze can feel quite chilly. If you're cold-natured at all, take some sort of light wrap with you.

Mid May will be warm but possible sea breezes or cool fronts could make you need slightly warmer clothes than you are thinking of.

I’d go with a mix of lightweight pants and skirts/shorts. Short sleeve tops with a cardigan or sweater you can layer if it’s cool. Most places are casual and you won’t need anything dressy unless you prefer.
Clothes in a fabric and cut that is comfortable in the heat/sweaty. For me that means light, loose, and probably not 100% cotton.
Sandals that you can walk in for long distances are good.

Specific to Greece - many archaeology sights lack shade so a hat is helpful.
Beaches are rocky so some sort of shoe you can wear in the water is highly useful. Not a flip flop - those won’t stay on in the water but are fine if you just stay on land.
Church tourism isn’t as common as in Italy but still happens. You will need shoulders and knees covered for that.

I did this tour last fall. A hat is a good idea, but they sell them everywhere in Athens, a bit cheaper near Monastiraki but I think I paid around 10E for a cheap straw-like (it's really made of paper) hat from a vendor on the street right near Syntagma square. I also bought a pair of ALEADER Quick Drying Aqua Water Shoes which worked great for going in the water and are ultra lightweight.

I have to agree with others on water socks or water shoes. The beaches are rocky and there’s also a possibility of sea urchins. Some hiking sandals also work as water shoes so that’s a good 2-for-1 choice.
You’ll need a good tread because polished marble is slick.

Many Greek Orthodox churches are beautiful. The key word here is “orthodox” so that means conservative. You need to cover shoulders to knees in order to please. A light scarf comes in handy.

I also agree with a light sweater. Many restaurants are outdoors and on the water. The cool night air feels cold after a hot day.

Ok, got some tips. Thanks everyone.

This is a spring trip so I’ll recommend a packable waterproof jacket. This will also cut the wind when you are near the coast. I always bring an ultra fine silk tee to wear under my tops when the weather turns. It is very compact (will fit in a quart size zip loc) so is worth the space.

You may want to bring a cute rash guard top and cute bottom instead of a swim suit. This is dependent on your desire to swim. But I saw a lot of sunburned tourists. The rash guards can integrate into the rest of your travel capsule wardrobe. This years styles should be showing up soon.

Several people have recommended good hiking sandals. I thought hiking shoes were a better option. There is a lot of walking on uneven paving so you need good traction. Some of the sites have paths that are unpaved. Think about the grit and small pebbles that will get in the sandals. Good sunscreen and also lip balm with sunscreen. Prepare for both hot and humid and hot and dry.

Chani
I would recommend a good walking shoe plus a good hiking sandal/water shoe. Both need decent treads.

A walking shoe and sandal combination should cover all the shoes you need for the trip. Wear the walking shoe on the plane.

I found that I was wearing my walking sandals most. The only times I was in a hiker was when I was hiking.