Here's a scenario that seems to be very common around here.

You start a double century before sunrise. It's 40-50 degrees + wind chill. You go for, say, 2 hours in these conditions before the first rays of sun. Things rapidly heat up afterwards, stabilizing at 80 F in the shade by midday. Then it gets cooler, and you finish after sunset with the air below 60 (and you're so exhausted that you can't balance your core temp efficiently).
In this situation, I'd start wearing base layer, long sleeve jersey, leg warmers, jacket and full finger gloves. I'd bring a triangle bag that, by noon, would contain everything but the jersey (and be bursting along the seams).
However, very few people I see at doubles carry triangle bags.
What am I missing and how would you deal with this?