Luggage and bags:
I was happy to have brought a waterproof backpack. Without it everything I have brought would have been wet after the cruise to Skellig Michael!
Clothing/Shoes/Weather Gear: Hiking boots will help you climb the 680 stairs up to the top! Bring weatherproof clothes for the boat trip, I was soaked when we arrived at Skellig Michael because all the seaspray hit me. The boatmen normally have lovely army clothes to lend you when they expect a rough crossing though!
Toiletries and Medical Supplies: If you get seasick easily and you have some pills that help you maybe you would want to take one pill before going...
Photo Equipment: Take loads of films or memory cards!!!! You wouldn't want to run out of films in a special place like this! And a zoom is perfect for taking pictures of all the cute puffins!
Miscellaneous: There is no shop, no toilet, ... hmmmm ... actually nothing on the island!!! Be prepared!