A thin base layer top with short sleeves or a neck zip helps you keep cool and avoid overheating on the ascents. Trekking trousers may not fit ski boots, or be warm enough, so base layer leggings may be better. Good backcountry ski layers tend to be thin, breathable and quick-drying to cope with changes in temperature. Wear a proper mountain shell jacket, or a ‘soft shell’ jacket in drier conditions. A single pair of ski socks work very well for backcountry use. For ski touring, ski shell trousers often fit better over ski boots than mountaineering shell trousers, but it depends on the design. A warm hat and spare mountaineering gloves are essential. A ski or mountaineering helmet is recommended, which can be swapped for a baseball cap on easy terrain to give UV protection. Your avalanche transceiver is far better worn at the start of the day, than packed in your rucksack! A neck gaiter can be a handy and versatile thing to wear (eg: Buff).