"Some of my clothes are cotton. Shhh...don't tell anyone."
As long as you know not to wear them and/or have non-cotton items with you in cool, wet environments. In fact, I would prefer a cotton shirt for daytime desert hiking. Remember that wet cotton will drain heat from the body faster than being naked!
As far as gear I use that fits this thread:
I have an awesome tiny backpack I got for $7 from walmart. Great for a daypack, especially if you also use a lumbar pack (between the two I can carry a heavy rain jacket, a super light wind jacket, 3L of water, food, and the 10 Essentials). The tiny pack weighs 7 oz on my scale, hold two 1-L nalgenes side by side with plenty of room for food and rain gear. Link http://www.walmart.com/ip/East-Sports-Mini-Back-Pack-Rose/16877858 I have it in black, but wish I had gotten it in pink for higher visibility!