The M203! The pic is actually a M4 version, I think; the one I fired was a A1 if I remember correctly. I like the idea of carrying your own, personal artillery along with you. Gives you peace-of-mind.
I started a 'small' bushfire with one of these when the 40mm round I had fired hit the old tank chassis I was aiming at, bounced off and landed in some long grass.