Sunglasses, sunblock, photo filters!
Dress accordingly to weather. Check forecasts for ski and snowboard activities in Pas de la Casa and keep in mind that in the mountains weather can change very fast. I experienced cold, foggy and rainy weather in France and surprisingly enjoyed beautiful warm sun about 20 minutes away in Pas de la Casa.
Always take sunglasses. The sun in high mountains is always very sharp! Do not forget sunblock and do use it on time! Once I've seen a woman with severely burned face after only 1-2 hours on the sun in high mountains! Take and use various photo filters from the basic ones: UV in the mountains and polarizing filter which reduces non-metallic reflections of snow. More in my tourist trap tip. In colder season be prepared to use chains while driving. Snow storms at Port d'Envalira pass are possible even in September or May.