Welcome to the site Guy Mandude.
The one item to pack...hmmm...if you're a music fan, I wouldn't leave without packing your favorite CDs. Or better yet, a DVD disc that you can burn about 100 CDs on to.
You can get fairly cheap tailored clothes in Bangkok so I wouldn't pack too many clothes.
Not sure what the Mexican food scene is like in Bangkok but whenever I got home I always come back with no less than 4 cans of refried beans.
I can find tortillas and everything else for quesadillas and burritos in Korea but I have never found refried beans.
BTW, where were you teaching in California? What city/school?
eric