.... I've had a cel sent to me wrapped in a 
T-shirt.

hrm....and there was a cel I got that was just 
stuck between 2 large doujinshi X_x;;; no wrapping 
at all (wrapped in yaoi...)

Now .. one really "careful" way I've seen a cel 
packaged is ... it is put in one cel bag, sealed, 
and then put into a slightly larger cel bag, 
unsealed, and then put in some type of plastic 
baggie thing that is then melted shut o_o