Probably because you hadn't thought through the situation very thoroughly....

That is an excellent example of "prepper fantasy world" planning. It might be hard to determine in advance just what might be good items to trade. My wife's grandmother was on the losing side of the 1918 Russian Revolution and she and her husband fled across Siberia to Manchuria (birthplace of my father-in-law), Shanghai, and eventually the San Fernando Valley (DW's birthplace). Several times they traded sewing needles with the locals for food and other essentials.