I would put Artisan soap from Hong Kong on the list for Hong Kong 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. The reason it works is that it gives you a quick reminder of the trip without needing to keep a fragile ornament safe forever.