Yeah. I always make sure to hit a restroom before driving through a city. Few things suck as much as feeling the call of nature while you're stuck on surface streets in the middle of a big city. Where are you going to be able to temporarily park your car and where is the restroom.

In the less dense zones, it's just stop at the next gas station/mcdonalds/starbucks/whatever. Less dense than that, just run into the woods...