Originally meant as a form of greeting, as in "What's up?", but has since evolved to mean other things. What it currently means is somewhat of a mystery, however the latest use of the word is in the phrase "Happy Suppy Friday!" which does not necessarily designate the said day as a Friday.
Short for "supplement", usually referring to the act of combining different flavors of smokeless tobacco in one's mouth. This most often occurs when one person has reached the end of his/her can, but feels that the final dip is too small. He/she will then ask a friend for a suppy in order to bring the dip to a respectable size.
Me - Shit, I'm all out of straight. This dip is weak. I need a suppy.
Wife - Here you go, luv, have some of my mint.