I have learned that even if it’s hot out, I still need an extra layer for the bus because it’s freezing in the morning. Then once off the bus, even if it seem cool enough at the start of a morning walk in the peak of summer, it’s soon going to be sweltering so go ahead and peel those layers off in advance.
Jane's Lessons Learned 
Much easier to layer and carry stuff around than to shiver! I can always find someone in my party who needs a sweatshirt… usually her name is MOM.