1 extra pair of socks and 1 extra pair of underwear is pretty much it. I have been known to leave a full change of clothes at the truck though...some of our trips we drive 6 or 8 hours, and having something fresh for the ride home is awesome!
Ill take an extra baselayer shirt tops if im going for more than 5 days, or its really cold and i might want a little extra warmth. Anything more then that and a pair or socks and underwear is not needed for me atleast.
Your going to stink, no amount of washing is going to help. iv come to the point where i wont even carry baby wipes or deoderant anymore, it dosnt help. Merino will definetly help. But the dampness is something to worry about. All the more reason i will be carrying a Kifaru shelter and stove and dry my stuff out nice and quick.
When clothing stays comstantly damp, its going to start to stink quicker.