I keep a bottle of the green bio-degradeable "camp soap" in my truck door, and try to always have some clean water available, bottles or otherwise. I don't drink out of a bottle used for hand washing. I also keep some blue "shop towel" type paper towels in my truck for drying hands. It's been very handy over the years, especially with kids that like to dig around in the dirt and rocks at every camp site, or pit stop. It's been used after porta-potties at various venues too.
I keep a small bottle of the same soap in my hunting pack, and always try to have some water in reserve, specifically for cleaning up after field dressing, that I wont drink out of.