If you're traveling in civilization, you can get by with a base pack weight of 0 grams (0.000 lbs). This guy is going around the world with no luggage at all:
http://www.rtwblog.com/

Having watched some of his videos now, I can immediately see some improvements I think he could make:

- Microweight wool T-shirts rather than (his sponsors') synthetic to better deal with odor. Probably rather than 2 extras, he needs 0 extras.
- Perhaps 1 extra pair of underwear, or no extras (wash each night), rather than 2.
- I'm not a speedo guy, but I'd probably make an exception rather than go with no swimsuit. (Maybe declare this underwear too.)
- Again, he's sponsored, but a tiny musette bag (man-purse) or bum bag or something seems like it'd be much nicer than the bulked-out luggage vest.