Dress accordingly to weather. Check 10-day weather forecast for Andorra la Vella and keep in mind that in the mountains weather can change very fast.
Always take sunglasses. The sun in high mountains is always very sharp!
Toiletries and Medical Supplies: 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!
Photo Equipment: Take and use various photo filters from the basic ones: UV in the mountains and polarizing filter which reduces non-metallic reflections of snow.
Miscellaneous: In colder season be prepared to use chains while driving to Andorra la Vella. Snow storms at Port d'Envalira pass are possible even in September or May.
Luggage and bags: You will need to bring a rucksack, sun protection for everybody... it doesnt matter if you have a good tan, you will need it!!!, sun glasses, sport clothes... you know... full equipment to go to the mountain.
Bring good tough shoes with a firm grip. Snow on the sloping footpaths could cause you to slip & fall in the street.
Toiletries and Medical Supplies: All main European brands are available here at duty free prices if you need them