Broken: 2.79, 2.91.0
Short description of error
bpy.data.fonts.pack() seems to work, and it even displays the "Packed Item" button next to the font name selector.
"File" > "External Data" > "Pack All Into .blend" also apparently works, but it also grabs images and other data.
Why not expose the "Pack" button for each individual font, to allow more granularity in packed and external data?
Exact steps for others to reproduce the error
Create any text object with any font.