Basics — documents (passport/ID, copies), credit card+cash, electrical adapter (Europe type C/E), personal medications, insurance.
Summer
Light cotton clothing, 2-3 swimsuits, sandals and walking shoes, SPF 50 creams, sunglasses, hat. Rain jacket for storms.
Winter
Layers — thermal shirt, sweater, waterproof jacket. Warm shoes. Gloves, hat, scarf. In some regions snow aids needed.
General
Small first aid kit, phone charger with powerbank, day backpack. The ForAll portal has detailed lists adapted to local weather and activities.