Maybe even a photochromatic pair of prescription glasses that change from dark to light for skiing in variable light. Flash coatings and gradient reflective coatings essentially reflect heat and glare from the sun and snow back on itself in the same way a mirror would, relaxing the eyeball and providing greater comfort. They also enable rain to bead and snowflakes to instantly break up on contact. If you look closely at the reflective coating found on some sunglasses, you'll note that they appear lighter across the middle than at the top and bottom. The major feature that separates cheapie sunglasses from truly performance-oriented specs is polarization.
Polarization is a thin wafer-like film that is sandwiched between two layers of plastic.
If you're not a prescription eyeglass wearer, chances are you'll find glass lenses a bit on the heavy side. Plastic, while cheaper, tends to scratch easier unless treated with an external coating. Glass lenses can shatter upon impact. Even if you don't need RX lenses, consider purchasing sunglasses from an eyeglass store or optical dispenser for better service. Many of these stores carry the same high-end designer eyewear that specialty shops do, and are better equipped to handle technical questions.