When I think of an easy, crowd-pleasing thing to bring back from Russia, buckwheat groats is a good pick because it does not need much explanation when you hand it over. Grains, pasta and rice are not glamorous, but they are useful, cheap and often taste different from the UK supermarket version. I would look for it in a proper local supermarket, covered market, deli, pharmacy, gift shop or small producer rather than leaving it until the departure gate. Back in the UK, it is worth checking specialist shops first because they often stock a better version than a broad marketplace listing. I would rate it higher when it is locally made, clearly labelled and easy to use at home, and lower when it is just tourist packaging.