Start with the basics...skis, boots, helmet & goggles!
Stay dry and warm with gloves, neck gator, long underwear, ski socks and jacket. You should always have extra of everything as well as an extra set of clothes in case your athlete gets cold or wet.
Hand warmers are also recommended on cold days. You can always throw them in the backpack in case your athlete is cold. Hand warmers can really turn the day around!
Each program will require different equipment beyond the above and will be communicated from the athletes coach.