Layers are the most important thing when it comes to staying warm and dry. Bring extra layers too. Start with a base layer of wool. Avoid cotton because cotton never drys and will only make you colder. Have a mid layer next, something that will keep you warm. Next have either a warm insulated jacket or if it's raining, a shell. Make sure you wear a hat as well, and even gloves if you want. Make sure you have waterproof shoes and wool socks to ensure your feet stay dry and warm. Extra socks are never a bad idea.