I can't think of much to add that hasn't already been mentioned by others. The orange vest and lights are a great idea, I agree there. I would say: use the practice runs to get an idea of what spare parts to bring along. Without a doubt you'll need a spare tube or a patch kit, or both. Spare spark plug (doesn't weigh much). Spare lighting supplies (bulbs, batteries if the system uses them).
My personal tool kit: spare batteries, spare bulbs, air pump, patch kit, dogbone wrench, light adjustable wrench, the two allen wrenches my bike uses, flathead screwdriver, phillips screwdriver, sparkplug wrench, miniature battery tester, clip-on LED emergency lights, test leads with spring clips (for emergency by-passing of broken electrical connections.) I think that's everything I carry. And each was selected to be fuctional but small and light-weight too. Everything above, and more, fits into this little box/trunk I have on my rear rack. With room left over to pack a lunch.
One last thing - YES! definitely, if you can manage it, take lots of pictures and document your voyage! There's a lot of us who'll want to see and read all about this. It'll help some of us make trips like this ourselves.