If you are going to one of the black sand beaches (Perissa, Kamari, etc.) be aware that the sand can get VERY hot. Obviously, in the middle of summer it will be the worst, and you will definitely NEED a bamboo-type of mat to lay on. Towels will not do.
Toiletries and Medical Supplies: Aloe Vera, Sunscreen 30+ SPF, the norm
Miscellaneous: Lots of water. More than you normally would think. With the black sands sucking in the suns rays towards you, the heat follows, leading you to quicker dehydration and chance for heatstroke or heat exhaustion.
Sorry, I am a physical therapist. I sound like a mom, don't I? Whatever. Stay alive and keep your skin!!
Be sure to bring comfortable shoes -- good for walking and climbing on rocky ground and the many, many stone steps.
Toiletries and Medical Supplies: Don't forget the sunscreen!
Photo Equipment: Bring a media card with LOTS of capacity if your camera is digital. Film was available in the towns, but I don't know how expensive it was. In any case, you will surely need more than you think.
Luggage and bags:
Smaller case the better, you will have to drag it up the steep streets otherwise.
Clothing/Shoes/Weather Gear: I went in July and my friend found she got a bit cold in the evenings, and it gets a bit breezy. Dare I mention a cardigan type of garment?....and she never wore her heels once due to the steep cobbled streets.
Toiletries and Medical Supplies: Sun tan lotion of course, gets very hot.
Photo Equipment: lots of film
Camping/Beach/Outdoor Gear: The sand on Kamari beach gets very hot, so flip flops are a must getting to the sea.
Luggage and bags:
Bring a backpack if at all possable, wheeled luggage is not fun on cobblestone streets and lots of stairs to get anywhere.
Toiletries and Medical Supplies: Sunscreen is very expensive, bring it with you to the island or at least buy it in town, at the beach you'll pay almost twice as much as in town.
Toiletries and Medical Supplies:
Your choices are this: Sunscreen or painful skin cancer that can kill you or make you regret living. I would shop the cheap stores at home before you leave. Its very expensive here!