Does everyone already know this? I only thought of this last summer.
Our first purchase in Paris (after some food, of course) will be BABY WIPES!
Carry a few in a ziplock to wipe your sweaty brow, the back of your neck, and--MY FAVORITE--your sweaty feet.
They are amazingly restorative.
And, from Mr FS, DUCT TAPE. This can be hard to find when you need it. This serves many purposes, of course. We are mainly taking it for SHOE EMERGENCIES. In Chicago many years ago, my sandals fell apart. Disaster! I didn't want to buy new shoes because I am a well-known cheapwad and hate emergency purchases. Besides, I have troublesome feet, so I can't buy just anything.
Eventually, we spied a store that stocked those cheap Chinese Mary Janes, which saved the day. Now I always carry extra emergency shoes on walks. But we also carry the beloved DUCT TAPE.
Mr FS wraps some around a pencil. What can I say? He is a genius.