Singapore
I would put Kaya jam on the list for Singapore 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.
Singapore
When I think of an easy, crowd-pleasing thing to bring back from Singapore, Singapore laksa paste is a good pick because it does not need much explanation when you hand it over. 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. 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.
Singapore
TWG tea tin is worth adding because it feels like something you actually noticed while travelling through Singapore, 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.
Singapore
This is exactly the sort of thing I like bringing back from Singapore: small enough to fit in a bag, but specific enough to remind you where you bought it. This is one to research before packing. If the rules are unclear, treat it as an idea to buy from a legal UK importer instead. 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.