To be quite honest, I would most likely NOT bring
my cels to a convention (especially the expensive
ones) because they could get damaged or stolen on
the way.  It is best to just leave them at home,
in my opinion at least.

If you HAVE to bring a few cels or sketches, try
to pick ones that people generally don't see on
the internet (a rare shot of a rare character) or
from titles that are new or currently popular such
as Naruto, Alchemist, etc.

But, as I mentioned in the first paragraph, I
wouldn't bring any.  I would just give them a link
to my website to look at my cels and sketches
since that is the safest and easiest.