I have some friends in from out of town for the Fourth and they've heard so much about Boston's celebrations that they're dying to go.  The problem is, I'm the host and I've never braved the crowds to go to the Esplanade for the 4th!  Does anyone have any advice on how early we should show up, what to do and/or not to do, and what we should and shouldn't bring?  I saw that the oval opens at 9 am, but I imagine the die-hards get there earlier and line up for their spots.  Is it worth getting there really early to get a spot in the oval or are the spots along the Charles as much fun?  Any tips are appreciated!