I pretest everything I pack for it's ability to wash and wear. I take three pairs of underarmor underwear and three identical pairs of socks (in case I lose a sock or two) that dry well overnight. I pack two or three t-shirts that can be sink washed and hung dry overnight and two or three button up shirts for a total of five. That includes what I wear on the plane.
I normally wash a pair of underwear, pair of socks and an occasional t-shirt daily. Button up shirts and pants, although also picked to hand wash/dry easily, are usually worn several times and laundered at a laundromat every couple of weeks. I bring a Tide stick for the occasional spill.
My wash technique is to use a very large zip-lock bag as my "washing machine" rather than just using the sink. I think mine is a Hefty big bag, probably about 2 gallon size. I tend to make a mess around the sink just washing my hands so the bag helps me keep things neat while I vigourously shake my clothes clean and rinse several times.
For warmth. I have found several really nice washable wool sweaters that can either be hand washed or laundered. My favorite came from LL Bean on clearance at the end of the season. I also pack a lightweight (100 weight) full zip fleece jacket that washes and dries easily. I also have some polyester sweaters but I'm now avoiding them. Layering polyesters tends to create a lot of static electricity, I like to put a layer of natural material(silk, wool) between layers of synthetics.