What you wear depends a lot on the season. Something to keep you warm when you take a break is good to have. If you get too warm, vent excess heat immediately and put your jacket in your backpack.

By combining the right layers you can wear and pack a reasonably small garderobe with lots of flexibility. Your clothing should provide comfort, warmth, and protection from wind and rain. You should be able to survive in the lowest possible temperature of the season. Pack a handful of socks and change them. A worthy multi-purpose item is the Särmä TST Thermal Cloak. Remember your head, neck, and hands too.