By at least one new pair for your next tour or bikepacking trip and I guarantee you'll end up wearing them the entire trip taking them off only to wash them.
I came to this conclusion after riding the skyline and blue ridge parkway last January but somehow forgot the lesson while biking the NCT (north country trail) in Michigan the last couple weeks. It has been unseasonably cold and very wet.
Disclaimer: I am not a Smartwool rep, nor do I even sell them. I just love their socks.