Turkey runs cold-and-snowy in Cappadocia winter, hot-and-coastal in Bodrum summer, and there's a mosque dress code regardless of where you go. Here's the season-by-season list.
You'll visit at least one mosque. Pack:
Best Turkey weather. Pack as if it's spring in Italy: layers, light jacket for evenings, breathable trousers, walking shoes. Cappadocia gets cold at night even in May — pack a fleece.
Cheaper to buy in Turkey than to pack: cosmetics (Turkish brands are good), pashmina/scarves (Grand Bazaar), Turkish bath products, fresh-roasted coffee, baklava. Don't buy: anything from the airport duty-free that you can get in a city for half the price.
Activate these from home — cheaper and simpler than sorting them at the airport.