Ugh. I like to wet a washcloth under cold water and then drape it on my face or on top of my head. Or wet a handkerchief and wear it under your hat (if you wear one). Luckily, I don't have to work outdoors, but I don't have air conditioning and sometimes it's hotter inside the apartment than outside!
I think the worst part for me about the summer heat is the drastic change in temperature: going from 90 degree heat outside to a chilly 65 degrees in an air conditioned building. Some places are just TOO cold, so I carry my sweater around with me at all times, especially at the library where I work.