One concrete example of Federalism I like to use with my kids are teacher's class rules. So the kids are going daily from class to class and sometimes the rules and expectations of their science class are very different than the expectations of their English classroom. And then on top of that there's the school rules that all teachers have to enforce.
I try to use this to draw out from the idea of reserved powers. Rules like classroom seating is one that would be silly for administration to try and do. It's like the state governments. But something like dress code is a school-wide policy because it's something crossing over "between states".