Sorry John, I don't really mean to destroy your allusions, but you should be doing a ride like this to enjoy, rather than thinking about speed.
You must take what you think will make yourself comfortable. I'd suggest, at the least, TWO tubes, plus 5 patches and a fresh tube of cement; a multitool of some sort, plus or inclusive of tyre levers; protection from cold and rain (a jacket?), and at least a handlebar bag, or a trunk bag mounted on a rear rack, and at least something for the inevitable sustenance you will require (ranging from banana to various packages of gel or powder or bar).
I tell you what. Weight your bike. Then add the weight of a handlebar bag, or a trunk bag and rear rack. Maybe 5lbs? Then the stuff you might put in it... maybe another 5lbs? Probably means your bike will weigh, what, 22, 25, maybe even 30lbs, plus the 10lbs of additional stuff.
Now weigh yourself. Factor that in as the TOTAL weight you will be pushing. It's probable than any increase in TOTAL weight by adding a bag and rack and bar bag and the stuff inside will be a small percentage of the weight you're already pushing.
You are showing symptoms of weight-weeniness! If so, you should be racing instead of doing a tour.