The biggest thing I learned about traveling when we spent six months on the road in Southeast Asia was Bring Less Shit. No matter how much shit you have, bring less. I wound up with extra room in both my pack and daypack, but I still think I'm bringing too much. I could certainly do with one less cotton T-shirt (or none!) and pair of underwear. With a little more winnowing, I could have traveled with just the daypack, which would be a dream.
