I normally have up to €200 in cash which I either buy at home or have left over from the last time. But I have a Wise card which I use to tap and pay, and use that for most things. I always have cash left over, and particularly large-denomination coins are handy, and I just keep it all for the next trip. With Euros there is always a next trip. But the best exchange rate will be from a bank-owned ATM in town, not at the airport, and I would avoid a situation where you have to get money out at the airport for this reason. Probably it is not the best rate at your local bank or currency exchange bureau in your home city either, but at least you can shop around a little and just limit what you get out before you get to Ireland.
Honestly the cash will just be emergency funds, most places nowadays card is perfectly acceptable.
Lavandula