I pick up current copies of the Tribune, the Sun Times, the Wall Street Journal, the New York Times, whatever looks appealing (and available) from DC and LA, perhaps a magazine or two. I place my collected goods on the counter, then put a bill or two summing half again the price of the stack on top, and rap it with my fingers to draw the vendor's eye. When he looks, I slash my hand sideways to indicate I need no change, and he smiles, takes the money, and thanks me. I gather my purchases and go on my way.
The vendor may have any number of opinions of me; he may think that I am tall, or gangly, or quiet, or generous. He may think that my clothes fit badly. But it will never once occur to him that I might not be human.
As I said, it is a guilty pleasure.