The term Six Demon Bag comes from a line in the movie Big Trouble in Little China, and refers to a sack that contained the magical tools/potions of Egg Shen as he led Jack Burton, Wang Chi, and the Chang Sing in their desperate attack against the evil Lo Pan.
Egg Shen: Can see things no one else can see. Do things no one else can do.
Jack Burton: Real things?
Egg Shen: As real as Lo Pan!
Jack Burton: Hey, what more can a guy ask for?
Egg Shen: Oh, a six-demon bag!
Jack Burton: Terrific, a six-demon bag. Sen-sational. What's in it, Egg?
Egg Shen: Wind, fire, all that kind of thing!
Typically used to describe something that whips alotta ass.
Jack: That loot ninja just ran off with our +7 sword of fire after we did all the work bringing down that TetraHydra!
Egg: Yeah, I'm going to open up a six demon bag on his ass!