We took this tour in late October. It was awesome. Everyone's clothes were casual and comfortable. It was still warm with highs in upper 70s to low 80s. For sun protection, bring a hat!
There are lots of stairs. And at Segesta you'll walk downhill along a path from the Greek theater to the Greek temple. And the temples at Valley of Temples are quite a distance from each other. If you can work your way up to walking at home 2 to 3 miles several times a week and can do some squats, you'll be able to do this trip easily. Wear comfy shoes. Husband wore Nike running shoes. Wife wore Asics with max cushion sole.
We packed clothes made of technical fabrics (polyester & spandex or light merino wool blends) that could be hand washed and hung up to dry. Typical brands included Columbia, REI, Kuhl, Eddie Bauer, Under Armor, SmartWool, etc. (Lots of things bought at TJ Maxx, Marshall's, Sierra Trading Post, REI, Kohl's.)
Including what we wore on the plane, we had:
HIM - 4 pairs technical fabric "hiking" type pants.
HIM - 4 long-sleeve lightweight pullover shirts. 1 long-sleeve light merino wool shirt for Mt. Etna (cooler temps at higher elevation). 4 short-sleeve "t-shirts". 2 Columbia long-sleeved button-up shirts for sun protection.
HER - 3 pairs technical fabric "hiking" type pants.
HER - 2 long-sleeved lightweight pullover shirts. 1 long-sleeved light merino wool shirt for Mt. Etna. 4 short-sleeve "t-shirts". 3 Columbia long-sleeve button-up shirts for sun protection. 1 long-sleeve light polyester "dressy" blouse (worn only twice).
We also had lightweight windbreakers, light gloves, and knit hats for Mt. Etna (also hilltop town of Erice was cool, windy and misty). Mini travel umbrellas came in handy on last day when it rained hard (with thunder).
Some people also brought shorts and bathing suits for going swimming in the sea (on your own, not part of tour).
We hand-washed a few things in the hotel sinks twice during the trip. All tour members wore outfits multiple times. No big deal!
All hotels had shampoo and hair dryer, but not conditioner. (And they don't have washcloths. Just use your hands.) Also, shower floors were very slippery. Next trip we're bringing flip-flops as shower shoes. We really enjoyed this trip and hope you will too!