Where do i start?
Layers, Layers, Layers. It is a lot better to wear three lighter tops than a big jumper. You might look daft but it keeps the cold out.
You also might like to think about take a spare change of clothes with you and leaving them in the car (If you have one). Ive been soaked through too many times without a dry set of clothes and its not the nicest feeling ever. Never hit the slopes without a sufficient supply of painkillers about your person. You might not need them but you never know when someone else in extreme pain might be so gratefull just for a paracetamol.
Do not forget to pack a high factor sun cream. Just because its cold it doesnt mean you dont need it. A friend in April burnt all over his face and apparently it hurt. Depending on you level on the slopes you might be able to take a high quality camera out with you. If you are likely to fall over lots then there are now disposable cameras which have a rubber outer and are water resistant. Just the job for all the beautifull sunsets