I would carry some gels and energy bars in case you feel a bonk coming on. You may not be able to stuff that much food down at rest stops, especially toward the end when you are really tired. A sugary sports drink in one of your bottles is also good for a quick boost of simple carbs.
Biggest thing about riding in a group is don't overlap wheels with the guy in front of you (
http://www.bikeforums.net/showthread.php/758510-I-think-this-says-a-lot...A-LOT!). Try to keep your head up and scan the road ahead instead of focusing too much on the person in front of you (or worse, his back wheel). It'll probably spread out quite a bit after the start, just find a small group you can comfortably ride with.