Hanging out is definitely allowed. There isn't really any ridged structure outside of pitching and organizing teams. And even then nothing is set in stone.

If you're a developer or designer I'd definitely recommend hanging around, they always seem to be in short supply. 54 hours isn't a lot of time to start a company so teams will take as much help as they can get.

As for an idea that's 'too big', if you're really in love with it and want to pitch it I'd recommend segmenting it. Try to find a feature or a subset of features you could build in a weekend with a team. SW is what building a startup would be in a perfect world, where you have everyone and everything you need right at your finger tips. But it only last 54-hours, so capitalize on it while you can.

Also, if you need help with your pitch just tweet before the event using the hashtag and ask for help. That's what I did and I got people (namely @JoshSamBob) jumping in to help even before it started!