My main advice is to NOT panic; really, as you're doing this to have fun, right? No reason at all to panic on an organized ride, IMHO; as the other responses noted, you'll find that the route is more than likely marked with "Dan Henrys" (those directional arrows on the right side of the road to alert cyclists to upcoming turns or, in the case of a busy intersection, to confirm that you should continue straight through it); that the organizers have either done this before, so that they know how many riders to plan for - estimating how many day-of riders will show up in addition to pre-registered riders and they'll stock the rest stops accordingly. If there are snacks and electrolyte replacement drinks that you are used to having, then by all means, bring your own. I also find it helpful to prepare as much in advance as possible, in case I have to get up at o'dark hundred to get to the ride start, I'll set out my clothes, put my drink bottles and/or camelback on the kitchen counter with my snacks, have my bike and gear on the bike rack/in the car, etc...(I've volunteered at packet pick-up or ride registration for quite a few rides with our club and have been surprised at how many people show up to go on a ride without filled water bottles, no helmet or un-inflated tires; guess they just expect that there will be someone to help them at other than a rest stop?).
I'd agree on waiting until after you've finished riding to head to McD's...by then, you can sit and eat, relax and enjoy it, rather than knowing that it might affect your riding performance and how you feel if you eat heavy in the middle of a century.
One other thing, I looked at some of the pics too and I'd caution you to be very careful boarding and exiting on those slick metal ramps for the ferry...
Have tons o' fun!
Tailwinds!
Mary