I went through Sadakhlo several times when I was going by marshrutkafrom Tbilisi to Yerevan. As it's the main frontier post between the two countries, it's almost inevitable you will go there.
Apart from the long hours spent waiting to obtain a visa from the Armenian guards, the sunflower seeds shared with the other passengers who were also waiting, or a few jokes we exchanged with the soldiers, I don't have any memorable souvenirs of the frontier village of Sadakhlo.
The contrast between the transfrontier comings and goings, often from capital to capital, and the deprivation of the region's Azeri peasants, with their donkeys and carts, made a real impact on me, not to mention the village's frontier market which was very lively but also very poor. For visitors, Sadakhlo is just a somewhat strange short stop, a bit of Azerbaijan to have a stamp between Georgia and Armenia,the south Caucasus in miniature ...