(2) A slang term for Marijuana: Cannabis
(3) A term meaning pulling on something forcefully.
(2) "Hey, I heard the cops arrested Jhonny because he was selling reef. I can't believe he would do such a thing."
(3) "Stop reefing on that pencil, or you will break it"
It would require pulling on a rope which would have been made of hemp (oh yeah, same stuff, it made good rope as well) thus the terms "reef the sails", or, "reef her up", or even cowboy slang meaning to jerk harshly on a rope when team roping.
Reefer as far as convenience store Coca-Cola goes must mean a refill, hardly as colorful a term.
Talk about dumbing down.