If you are coming for any tours of Ireland then remember that currency in the North is different from the South.
In the South ( Dublin , Cork , Galway , etc ) the currency is Euro , while in the North the currency is Pounds Sterling.
Often we have clients who bring one or the other and it is useful to have both.
Whilst the hotels and restaurants generally take credit cards there are those smaller local businesses that do not.
Sometimes these smaller restaurants and pubs are the very ones that you wish to visit , and sometimes there is not a cash machine nearby.
So when you are coming to Ireland and you plan to visit North and South make sure that you have the correct currency for both zones.