If I had worried about all this stuff, I would have never been on the road! Guess someone was looking out for me!
Helmet is a pain to carry, but I use a cargo net to hold it on top of the stuff in the passenger seat.
After my first 100+ degree day, I had a couple gallon jugs of water on board. Just kept pouring it on myself. Someone else had Ziploc bags of ice to put under clothing.
My plans changed and I'll be leaving from Washington State. Haven't looked at a route yet.