I would put Vinegar or infused oil from Comoros on the list for Comoros because it is the kind of thing that feels useful once you are home, not just another airport purchase. Oils and vinegars work well when the bottle is small, sealed and wrapped in clothing inside checked luggage. 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. The reason it works is that it gives you a quick reminder of the trip without needing to keep a fragile ornament safe forever.