kill 2 birds with 1 stoner

1.) To go shopping with a stoned friend for munchies and also pick up groceries you need.
2.) A situation where you have to run an errand and a friend tags because they either have something to do in the near where you're heading, want to pick up some weed from your destination, or both.
3.) A situation where a friend or friends are hanging out and toss money in to pick up some extra weed after finding out one of them already planned a deal for themselves.

A: Yeah, man. I'm about to pick up. He said he's about to head out the door in 10 minutes.
D: Mind if I kill 2 birds with 1 stoner and throw in some cash in to get myself some?
A: Sure, why not.

Eric: Me and Dave are gonna run out and pick up some food real quick. Do me a favor and save me a couple hits for when I get back sincr I haven't gotten a hit yet.
Dave: You hear him, we're killing 2 birds with 1 stoner. Let's roll.