what would you put in your backpack for 3 weeks?

this question is one that i've been thinking about a lot lately. We've decided that we'll only bring backpacks... and small ones at that. We'll carry everything on the plane for our 20 hour travel.
It really makes more sense this way. After talking to Miles (our friend and brother here that is helping us with our journey), we're going to be traveling a bunch once in Thailand and no one wants to lug a ton of stuff around. Kinda makes you re-think your Americanness. Do you really need more than 3 shirts and 2 pairs of pants? I'm not sure that we do. I'm happy to have this chance to take a step back from this crazy paradigm and look at things in a different light.
-james