Cambodia
I would put Kampot pepper on the list for Cambodia because it is the kind of thing that feels useful once you are home, not just another airport purchase. The best version is usually the sealed jar, tin or packet from a normal supermarket, spice stall or food hall, not the most expensive tourist version. The reason it works is that it gives you a quick reminder of the trip without needing to keep a fragile ornament safe forever.
Cambodia
Checked cotton scarf used as a practical everyday textile.
Cambodia
This is exactly the sort of thing I like bringing back from Cambodia: small enough to fit in a bag, but specific enough to remind you where you bought it. The best version is usually the sealed jar, tin or packet from a normal supermarket, spice stall or food hall, not the most expensive tourist version. It is also the kind of thing you can talk about when someone asks what you brought back, because there is usually a little story attached to where you found it.
Cambodia
Cambodian coffee beans is worth adding because it feels like something you actually noticed while travelling through Cambodia, rather than a generic souvenir. It is a good one because people can try it slowly at home, and it makes a nicer gift than a mug with a place name printed on it. The ideal version is modestly priced, not too bulky, and good enough that you would buy it again even without the holiday memory.