Try to hire as much stuff as you can, especially ski jacket and pants / salopettes. Hire of skis, boots and poles is probably included in the package, but check with your tour operator before you go. Other things to take: some thermal polo necks - at least one fir every 2 days, more if you haven't got access to a washing machine, you get v. sweaty! Thermal long johns, tube socks (seamless, so you don't get blisters). These are essential as ski boots are very tight fitting. Ski gloves can be bought for �10, as can goggles, though you may prefer to buy sunglasses (make sure they're robust and a good fit). Sunscreen is a must - Boots do a tube that is designed for winters sports and has a SPF lipsalve on the end - it's perfectly sized for sticking in your pocket of your jacket.
When looking for a jacket and pants to hire, look out for ones that are fitted, with lots of pockets. You'll need a pocket for your ski pass, gloves, sunscreen, money, hotel key, sunglasses. Also, try and get pants that have a side pocket (like combat trousers) that will fit a 500ml bottle of water. It is essential to keep hydrated on the slopes to prevent altitude sickness.