What to Expect (and wear)
It's called Foo Camp for good reason. It's much more casual, informal, and spontaneous than a typical conference. While there will be an amazing array of sessions to choose from every hour, it's perfectly acceptable (and not at all unusual) for Campers to spend time in conversation rather than attend an organized session.
Foo Camp is a gathering of peers, though everyone's an expert in their particular field. We encourage you to bring your prodigious curiosity to the event, and predict that you'll learn as much as you share.
Sessions are usually very interactive and conversational. For tips on leading a Foo Camp session, read Scott Berkun's excellent piece, How to run a great unconference session.
As for what to wear–-go with whatever's comfortable. Bring layers (including a jacket), as the temperature can vary by 30+ degrees in one day, with chilly nights and hot afternoons.
Said elsewhere: get a lot of sleep beforehand. Foo Camp begins Friday at 5pm, and does not stop until 1pm Sunday. NON. STOP. There are discussions at 3pm, and at 3am. People leave for bike rides at 6am, and blast water rockets at 6pm. There is always something to do, and people to talk to. Arrive well-rested, and ready to sleep as little as possible.