Depends on what you want.

McDonalds is suprisingly handy. You can have an egg and sausaage muffin at breakfast time, dump the bun. Or have a regular burger or cheese burger, again dump the bun. Or the side salad or the grilled chicken salad is fine. If you are in Grafton Street in Dublin, then the Vienna Coffee in the McCafe is wonderful, and made with proper cream, not sugary junk.

Avoca food hall, and Fallon & Byrne as well as a few other places, do Lindt 99% chocolate. This is great stuff, very low carb, amazing chocolate taste, but so strong you are happy to eat one or two squares and stop. It's also a great ingredient in things like low carb chocolate moouse. JC in Swords have it too.

Holland & Barrett have some useful stuff. GG crispbreads are very high fibre, so they fit well on a low carb diet. Flaxseeds are a great ingredient for making your own low carb bread and cakes. Whey protein powder is a useful ingredient in things like low carb icecream.

I do a lot of my shopping at the farmer's market in Temple Bar on Saturdays, lots of interesting vegetables and organic eggs and cheese there. Tesco is good for cheap nuts.

Things like John West Tuna with a Twist or a stick of pepperami are good to carry with you.