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This list is aimed at multi-day hiking with the possibility of some high-altitude hiking. Consider two pairs of socks, if one pair get wet it can be very uncomfortable. When hiking at high altitude also consider a backup pair of sunglasses. They don't have to be expensive but if you break your sunglasses when surrounded by snow you may suffer from snow blindness and have to abandon your hike. It's a good idea to take a spare set of boot laces, these don't weigh much and can really help if one breaks on day 3 of a 12-day hike. Even if you feel water isn't an issue it doesn't hurt to have water treatment tablets available. They won't weigh you down but can save your life if you find a water supply you were expecting isn't operational. Down jackets are fantastic for very cold temperatures. It's often a good idea to have a lightweight down jacket at least for evenings. Down jackets are considered an essential item for high altitudes. Down is commonly made from duck or goose feathers, the jury is still out on which is the best.
