Even when packing light you should carry a set of 'dry' clothes as either a backup for for sleeping in.
I guess that's another reason to avoid cotton...I'll take soaked poly or wool any day over cotton.
+1
I can't think of a reputable outdoor or active lifestyle apparel company off the top of my head (North Face, Columbia, ExOfficio, Under Armour, etc.) that offers anything that's manufactured from cotton -- everything seems to be nylon/polyester/poly blend, and for good reason.
Before moving to North Carolina we lived in SoCal, and I used to head into the mountains (lower elevations) from time to time wearing a cotton trekking shirt and jeans, but except for very rare exceptions, we'd also go 9-10 months without a chance of rain.
One only has to compare the time it takes when doing laundry to see the difference poly makes. My lounge-around-the-house-or-wash-the-car-in-the-driveway cotton t-shirts take close to 40 minutes to dry on medium heat. My wilderness/outdoor gear is virtually dry enough to wear as it comes out of the spin cycle in the washer, let alone a few minutes in the dryer on the "cool" setting.
The very first thing that struck me when I initially watched a few instructional video clips of Ron Hood on the internet was the fact that he was wearing denim jeans. If not for the reputation that he had established for himself over the years, I probably would have written off his advice based solely on that fact.
Other than perhaps a bandana around my neck in the summer (that I want to stay wet all afternoon) or when flying (to avoid having a jet fuel fire resulting from a crash melt all my clothes to my body) I've limited the cotton in my backpack to Q-tips and PJ impregnated cotton balls.
Jim