If you were teaching data viz and part of the class used ggplot2, what ggplot extensions would you cover (either teaching, or just mentioning for interested students)?

So far:
ggrepel, ggridges, directlabels, gghighlight, gganimate, ggthemes, patchwork, plotly

With caveats:
1) Won't have time to cover maps in ggplot, those will be done in other software, so no ggmap/etc.
2) ggplot is only part of the class, so I can't cover everything under the sun
3) I'm also covering palette packages like RColorBrewer, I didn't list those