The answer has to be toilet paper. Eating utensils were important in the development of civil society - it's hard to have a state dinner in your finest garb if you're sloppily tearing food with your bare hands after all, but toilet paper, or something other than just grabbed leaves, is essential for civilization to flourish.

Let's delve into the analysis here. A society isn't truly civilized until you're using the restroom inside. If you're roaming the wilderness like so many wild beasts looking for a nice, secluded place to squat, there's nothing separating you from a caveman really. Now, it doesn't make any sense to use the restroom inside if you first have to go outside to gather implements with which to wipe yourself clean. Therefore, toilet paper, or at least toilet cloth, or gathered/collected leaves (which would be the simplest form of toilet paper) are a necessary prerequisite for having indoor restrooms. You can't have a nice state dinner in your finest garb if your guests are forced to hike it to the bushes for potty breaks either, and having indoor restrooms is a bigger step than having eating utensils. Therefore - toilet paper brought us indoors and severed one additional bond with the outdoors, a crucial step towards where we are today.