I think the Laffer curve(particularly how it varies in width depending on whether it is a corporates, sales, or income tax), the various types of taxes, the basics of supply and demand, gold standard/bimetallism, unemployment, and inflation would be enough.
Gold standard / bimetallism - you mean for talk of history? Of course now we have fiat currency so that is a topic more for understanding historical contexts. I think it would be definitely relevant for high school as you go more in depth in history to look at various economic and political events.
I think that topic is a bit rich for a middle schooler personally - particularly a 6th grader for whom a great deal of the vocabulary used in the historical and financial accounts is complicated.
Laffer curves....
But I guess if it is a visual representation of the impact of a tax, subsidy, etc then it could be OK - a bit skeptical.
Inflation is a valuable lesson.
Unemployment - its a complicated subject to teach all the underlying issues - since the reported numbers can be doctored to not show the full story.