So if you don’t want him to stuff his pockets, I would recommend getting him some pants without pockets in them. He might then start putting things IN his pants, but it is worth a shot. Honestly, I would say, in the grand scheme of behaviors, pocket stuffing isn’t too bad. If it drives you crazy, though, maybe get him a bag where he can stuff things instead. Kleenex sells these little tissue packs at the dollar store that you could pick up. Perhaps you could load his pockets ahead of time with clean tissues, lock up other papers, and see what happens. If he can’t get to other paper he won’t be hoarding it.