I usually look on Google Maps for locations of Starbucks, McDonalds, BK etc that are close to the areas I would be so I know where there is a bathroom if needed. However, some Starbucks stores do not have bathrooms as they are not permitted as restaurants but as takeout-counters.
Another reason I look for these places is while travelling with my highly picky, allergic mum. These places offer something she can safely eat with minimal complaining.
I don't think it counts if you just use the McDonald's bathroom w/o buying anything.
I'll admit I've gone for breakfast since parts of Europe don't seem to do breakfast at restraunts. (Outside of super expensive ones in hotel)