Steve, somehow I’m guessing you cover that 100 miles faster than most of the rest of us. When I go out for a century, I’ve gotta pack for the long haul. (or just know where the stores are).
I like having some sort of saddlebag, though - someplace to keep the spare tube, multi-tool, etc. When it’s time to ride, they’re already packed. And yeah, w/some of those aero seatposts, it’s kind of a hassle.