I have seen these before. During my days at ASIO we apprehended 2 agents of the Japanese intelligent agency. We on both of these individuals a single satchel as you have described. After some vigorous interrogation (I wont elaborate) we discovered that these were actually "suicide" packets. They served a double purpose of being able to kill the agent if he was compromised and able to get to swallow them in time, but also to be completely water soluble, meaning they could be conveniently dropped into say, a coffee urn, killing all those who drank the coffee.
Or perhaps I've gotta stop eating things I found on the street...