The important thing to remember when skiing or any outdoor sport is that layering clothes is essential, this way you can adjust for heat and cold. It can be extremely cold in a snowstorm or at high altitude in January, but minutes later you can be in the sunshine and sweating.
Base layer - ( thermal underwear ) this is the key to keeping warm and also wicking moisture away from your body. 2 sets each, one on, one in the wash will keep you going all holiday. Take some washing liquid to wash them out with and hang them over the bath or on an indoor clothes line to dry.
Fleeces - wear over the base layer or add a T-Shirt as well. Cheap to buy, we usually take 2 each for Ski wear.
Ski Jacket and Pants - good quality ski jackets and pants can be found at reasonable prices, look for sale items, last seasons models, and look in discount stores such as TK Maxx or even Supermarkets.
Gloves - these are the key to a good holiday, don't skimp when buying them. Usually it won't be a problem when skiing, but when you are on the ski lifts that is the time you may get cold. Make sure they are waterproof, breathable and have good thermal insulation. Also consider liners for extra warmth, you may not need them but keep them in your pocket.
Neckwear - this becomes the valve with which you regulate your temperature. A buff is a very versatile option, replace your ski hat with it when it gets warmer or pull up over your chin and nose in the cold.
Ski Socks - buy proper ski socks not hiking socks. Designed for cushioning, warmth and comfort they are well worth the money. 3 pairs will do for a week ( wash out or wear twice ) they should also last many seasons.
Goggles - essential for poor weather and good visibility.
Sunglasses - if the weather is fine you will be more comfortable in sunglasses than goggles, hybrids are also available for the best of both worlds.
Helmets - Recommended for children and by law in some countries, don't let them ski without one. More and more adults wear them now, a sensible safety precaution so use your own discretion. According to a BBC news article, University of Innsbruck sports scientists say research has shown ski helmets reduce head injuries by 35% in adults and 59% in children under 13.
Wear your jacket when travelling to cut down on suitcase room and weight.
Choose clothing with plenty of pockets for money, gloves, sunglasses, lift pass etc.
Good gloves are particularly important for children, cold hands can make them miserable.
Wear something distinctive - It can be difficult to spot people in your party when in a croed, mist or skiing ahead.
Treat yourself by all means if you fancy some flash gear but don't feel that it is necessary, I have worn the same jacket and pants for 10 ski holidays that I bought in ASDA for £20 each!