What to do with all these souls?

recently i have managed to buy the souls of strangers...i do this by going to a nightclub and offer them a drink in exchange for their soul...they usually smile, sign and leave happy with a drink. i have around 30 now. i think they may come in useful after i die. i could proberly get hundreds this way. its understand it's a sinister thing to do; but i figured that they must be worth something if Satan is paying through the nose for them too.