I've been drawing live portraits at events for over a year now and it took me some time to figure out which materials work best and produce the most striking results in 10-15 minutes, dry super fast, are small and portable.
Here are my tools for live drawing:
Fabriano Hot Pressed Paper or Cass Art Watercolour Paper
Carbon Ink (fill in the old cartridges)
carbon ink cartridges (they will fit any brush pen, it did all of mine
And this is how it all looks in action! :)