I am always at a loss for napkins, especially after getting a fast food order to go. Often times I will wipe my mouth with my hand(s) is no one else is around.
This idea allows you to be polite, yet still allow you to wipe your mouth or blow your nose with your sleeve. Then, just tear it off and
voila! no social norms violated.
Also I would like to have full size paper towels on the bottom of my T-shirt for when I walk out of the men's room.
Come to think of it, toilet paper on the inside of your underwear would solve a lot of embarrasing problems. So when you're sitting on the john, looking around the room for a roll that isn't there, just reach into your trouser wad in front of you, and start wiping!