I don't do many sketches at cons. Mostly 'cuz I can't seem to sketch very well.
Instead, I roughly draw the pic in red line, then "ink" the pic using pencils. XD It still takes less time than inking does, and the picture quality isn't as dark as inks. But, I'll be damned if it won't be a good quality pic, regardless! ;)
Did this one for the ever patient xivk at this past AC. :)