Change is definitely another one that is hard. People these days really struggle with giving change when someone pays with cash. Actually, what really throws them is when you give extra change because you want to get a fixed amount back. Like say your bill is 11.23 so you give them 16.23 because you want to get a five dollar bill back. They can't handle it.
Yeah, I have noticed this too. I assume because most people use cards, combined with people's simple math abilities have dropped off a cliff.