Definitely depends on where you are going. For extreme cold climates consider mittens instead of gloves, and definitely take a spare pair of socks. Remember that what will make you seriously, uncomfortably cold is wearing non-breathable clothing that doesn't allow sweat to escape. If you are sweaty, you will get very cold, very fast, especially on the lifts going up. Hence the many positive responses here to merino baselayers, which wick sweat away and keep you warm. The spare socks are to change into at lunchtime if your morning pair are damp - a single pair of dry socks is significantly warmer than two pairs of damp socks. Clothing that allows you to regulate temperature can be very useful - i.e. zips that will help you to cool down when you start to overheat, and warm up when you start to cool down.