Just so you do not think it is only a "Sierra" thing, when in the Wind Rivers, I also take no second changes of clothes. I get up early and plan to stop by about 3PM. I rinse out my shirt and underware and let them dry between thunderstorms. I wear my fleece or raingear. I do not do this every day- but when the sun shines. Lots of time I take my "dip" in the streams on lunch breaks before the typical afternoon storms. I dry clothes on the top of my backpack while I am walking. Going without underware for a few hours is no big deal. Noon is also my standard time to wash hair. It dries quickly in the wind. Worst case of continuous cold, I simply stink the duration. I also never sleep in my hiking clothes and try to keep one layer mostly clean for sleeping. When the hiking shirt gets too stinky I wash it and put it on wet. It usually dries while I am walking. I wear long gaiters that really help to keep mud off my hiking pants. I wash the gaiters every day. I take 3 pair of wool socks and rotate them. One washed pair on my pack to dry, one on my feet and the other packed inside so I have dry socks at night. Of course, in the sunny Sierra this is a whole lot easier.