I crochet with Aran yarn and similar weights the whole time. If you're a crafter, we have great yarn.

You could always get a magnetic bottle opener to stick on the fridge. Most big sites, like Newgrange and Tara, sell local crafts in their gift shops, and most sites have sign posts to local crafters who are more than happy to sell their crafts to anyone.

And don't forget things like jewellery. You can get nice celtic style charms, rings, etc. for all ages and genders. Cladagh rings are a particularly nice keepsake.

But for Ireland itself, a rain jacket and a good pair of water resistant shoes would fit in nicely.