Wow. I take a clean pair of socks and undies, very lightweight PJs that also serve as long-johns when it is very cold, and a puffy down jacket. That's it. I wash the undies and socks every night to have a clean pair drying during the day. And I wear the same shirt and pants for at least a week at a time---sometimes washing the shirt in a stream.

In winter, add one more layer on top and bottom--wool long underwear.