I'm sure if you live in PDX you already know this, but Portland has some of the best (if not THE BEST) food carts anywhere.
Cheesesteaks, waffles, BBQ, burgers, Korean, Japanese, Greek... I could keep going.
I found a website that does a pretty good job at keeping track and discovering new carts.
Cheesesteaks and Burgers off of Pioneer Courthouse Square is definitely my favorite place so far. Close runner up is Mobster Meatballs up on College ST/4TH Ave.