I had an extremely hard time with this challenge. Since my work place is very casual, I try to wear my most comfortable clothes (usually the bummiest) when there's a heat wave. To meet the requirements for this challenge, I picked dressier but still light-weight items that are machine washable because the worst is sweating through dry-clean only clothes in the heat. The choice was between light-colored fabric vs. dark-colored fabric. With lighter colors, sweat stains are more visible. But with darker colors, you tend to sweat more. So... it came down to grossing others out or dealing with periodic waves of hot flashes? (Ok, I exaggerate, it's mostly not that bad) I chose the former.
For the commute: A tee, pencil skirt, and flats.
For work: Don a blazer and swap out the flats for a pair of pumps.