Part of the value would be that eating potential; the limited supply from the commissary plays into scarcity.
Let's see; the Comanche traded horses, rode horses, and ate horses. Horses had value even tough the value of individual horses "expired" from death or feasting.
Then again, horses had varying traits, and one packet of mackerel is probably the same as any other.
It's a really good point. Physical dollars get lost, ripped, and taken out of circulation by the Fed all the time. The rate that they put money into and out of circulation is largely unpredictable. Whereas with Mackerel its a lot easier to quantify. That was my experiment.