Maybe the gasket on the oil drain plug? I don't know of any other gasket that would relate to an oil change. I haven't changed mine yet, so I wouldn't worry about it.
Yeah, you are "supposed" to change that gasket, along with the oil plug itself I believe.
But anyways, either one of those can be picked up at Autozone for under a dollar if you want, although, I have never changed mine as of yet.
I would just change it if either are damaged, or if the gasket has a crack in it.