You want your inner layer to be wicking — no cotton. Next layer should be insulating and warm, and the top layer should be water proof but breathable. You will need clothes for hiking during the day, lounging in the evening, and for sleeping. Layers are important as temperatures vary greatly.
Your clothing should be lightweight, breathable, hand-washable, and quick-drying.
Be sure to break in your shoes before the hike!
Store electronics in sealed water-proof bags (double bagged if possible).
You really only need one first aid kit in your travel group, so coordinate with your travel companions.