35C around here today and this is what I wore to the Scottish Festival. I should probably note that our humidity is usually pretty low, which makes the heat more bearable. It generally doesn't bother me until it's at least 40C+ (my wife, on the other hand...)
I did make two concessions to the sun/heat; I usually wear a cowboy hat, and since I ran in the Scottish Sprint 5K earlier in the day I stuck with the running shoes.