I have VERY LIMITED experience with standing in line for 
autographs/art.  But I have found that the big cons with a line 
the size of a city block are unlikely to accommodate fans who 
want sketches, but the smaller cons the artists are really cool 
about drawings. As far as brining your own supplies, you have to 
bring something to be signed, they generally don’t give you 
anything.  As sharpies go, I was actually once able to jump to 
first in a line and get my cool Urd sketch, because I was the only 
one in line with a marker. (of course I left it so others could 
move forward)  So I guess the moral of my story is...... It never 
hurts to be prepared!”