Before you go, go
I was talking with Matt Rourke a while back and mentioned the importance of always carrying water and food in my truck. We never know where we'll be or how long we'll be there.
He agreed, but said he tries not to drink water during shoots. More importantly, he said he runs to the restroom before he scrambles to a breaking news assignment. These two facts are linked if you consider it.
He's right. It's darn hard to focus when you can't see because of the pain.
Once we're on location, we're frequently trapped. It's a matter of bearing the pain if we didn't think ahead. Consequently, it's better to be two minutes late than to miss the event because you had to (re)leave. More frequently PJs are "in position" (at breaking news) for several hours before something happens anyway, so it's time well spent.
Avoid taking the camera
Most of us know to visit the restroom frequently. An additional problem occurs on sports shoots or at public events. What do you do with the camera?
No matter how innocent it is to you, people give us strange looks if we march into a crowded public restroom with a camera. I think it would be even worse if this occurs in an area with predominantly children.
So, do everyone a favor and use the facility before you break out the camera. I typically tell the people at the gate who I am (without equipment) and tell them I would like to use the facility before I get my gear. They understand, and nobody gives me grief.
If the shoot is at a stadium, there's typically one restroom in the press box. Since you need to get rosters and such anyway, it's the best opportunity because nobody is going to mess with your gear while it's unattended.
Where are some other choice places?
Government buildings – particularly city halls – have nice, clean restrooms. City halls are typically labeled clearly on detailed city maps like those available in metro areas.
Gas stations are another likely option. However, some major convenience store/gas station chains don't offer public restrooms and others are just nasty.
Many public parks have restrooms as well. Most maps clearly show all the parks nearest your present location as well. But, these tend to be the poster-child of nasty. Avoid this option if possible.
Large banks tend to have really spiffy restrooms. However, I reserve this option for "special occasions."
More than enough for now,