Ireland
I would put Irish whiskey miniature on the list for Ireland because it is the kind of thing that feels useful once you are home, not just another airport purchase. For alcohol, I would only bring this back if it is sealed properly and comfortably within the UK allowance; otherwise it is better as a UK-buy link. The reason it works is that it gives you a quick reminder of the trip without needing to keep a fragile ornament safe forever.
Ireland
Barry's tea is worth adding because it feels like something you actually noticed while travelling through Ireland, 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.
Ireland
This is exactly the sort of thing I like bringing back from Ireland: small enough to fit in a bag, but specific enough to remind you where you bought it. Biscuits and dry breads are good because they survive the journey and are easy to share at work or with family. 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.
Ireland
Traditional knitted wool scarf or jumper inspired by Aran Island patterns.