Balaclavas are great for covering the head and providing a ton of warmth. Many of them are thin enough to slip under your helmet. While Neckwarmers are often a touch more versatile and slimline. Both offer protection that can be removed in a second if you start overheating.
Look for technical materials for the best neckwarmers. Mons Royale offer great Colourful Merino Wool options in the Double Up and Daily Dose, while Le Bent has a Bamboo and Merino Blend that is always soft on the skin.
Anon offer Neckwarmers and Balaclavas with inbuilt magnets that allow them to firmly attach to the bottom edge of their Ski Goggles and never budge. Check out the Lightweight Mens MFI Neckwarmer or Midweight Womens MFI Neckwarmer if you have a pair of their goggles that is compatible.
Small enough to slip in your pocket, never leave home without your Neckwarmer or Balaclava to protect you from the changing conditions at the snow.