That is the only souvenir I brought back from Afghanistan: two rocks. That is about all I could find while I was there, partly because I was in the hinterlands and partly because the country is impoverished to the point of having little of the range of normal "souvenirs" that I might bring back. There were some high end items, such as rugs and shawls, very modestly priced, but these are not the typical things I bring back. These are things specifically made for tourists, and I prefer back to bring back artifacts of daily life. So, I brought back rocks.
Yet, even had I been able to find some others things, I may have chosen to bring back rocks, anyway. There is something special about bringing back a rock: it is a piece of the land. There is certainly nothing more Afghani than a piece of the country's desert or mountains.
My catechism students understood this very well on some deep level. Last year when I went to Bahrain, I told them I would bring them back anything (within financial reason) that they would like. They asked for rocks! There were many souvenirs I could have purchased easily for them. Instead, one of my good Bahraini friends and I spent an extremely enjoyable evening hunting for the very best rocks on the beaches around Manama. (An island has no lack of beaches -- or rocks.) So, instead of bringing back a curiosity or tourist's treasure, for my students I brought back rocks, uh, a physical piece of Bahrain.
As for the two rocks I brought back from Afghanistan, they will proudly join the rock I plucked years ago from the Yambash River in Turkmenistan near the Iranian border. I may have left both countries, but with my rocks, the countries will never leave me. Now, what could be a better souvenir?