I had to go pretty bad this past trip to Europe. We stopped at the train station for a public restroom and of course, you had to pay to get in and I did not have any coins. Run to the nearest shop and ask for change. The guy taps the cash box and says "it's locked, see". Ugh, I happened to see my favorite candy - fruit Mentos, grabbed a roll and threw it down on the counter.
Got my change and into the restroom I went.