Travel tips needed

So in a month’s time I’m headed to Wroclaw, Poland for wroc_love.rb. This is the first time I’ve traveled overseas in almost two decades, so anything I ever knew about international travel I’ve forgotten. (Canada doesn’t really count as international travel. Sorry, Canadians.)

As an American nerd flying to Poland, what do I need to know? Any tips welcome, from must-know information about the red-tape and paperwork, to how to make my cell phone work, to foods to try and/or avoid.

And just what the heck is a “duty-free shop”, anyway?