There were porta-potties all over the bases when I was in Iraq, so we all got used to them. Nothing encourages rapid voiding quite like 120+ degree weather.

Public facilities were non-existent when we were on mission and even the most iron-bladdered can't hold it on a 10 hour mission. So, we used to pull off the side of the road in a semi-safe spot and take turns on lookout while the other person did their business. There was always a bit of coordination just prior to stopping about who would get what spot. Men to one side of the vehicle, women to the other, etc.

One night our gunner announced she had to pee outside of Fallujah enroute to Baghdad. Since we weren't going to be stopping for an hour or so, she decided to deal with the situation. She loosened her restraint harness and had someone spell her on the 50 cal while she took a pee off the top of a vehicle doing 45 mph down the very-bumpy Baghdad-Jordan highway. Didn't even get any pee on the vehicle.