I would put Artisan soap from Taiwan on the list for Taiwan because it is the kind of thing that feels useful once you are home, not just another airport purchase. Small bottles are best. A local scent, soap or oil feels personal, but it is still easy to pack and usually does not cost airport-perfume money. 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.