I second the comments about doing long back-to-back rides -- if I'm riding two centuries back-to-back, I work up to riding two 80-mile days in a row. If you do that, you'll find Day 2 feels exactly like any other training ride. My first back-to-back ride people kept asking "How you doin'?" or "How do you feel?" on the second day, and I honestly answered, "Great!" because I'd trained so much ahead of time.

Food/everything else: I don't have much to add (eat lots, eat carbs, drink lots; same routine, really, as after any other training ride) except that napping and going to bed early on the night between is really helpful. Also bring a very comfy pair of shoes to wear on that Saturday afternoon -- the first time I did it, I only had flip-flops and my biking shoes, neither of which were good for an entire afternoon of hanging out.