Clothing/Shoes/Weather Gear: A lot of the walks in the area are on rocky or marshy ground and there is often quite a biting wind blowing so take a windproof jacket, maybe a beanie to keep your ears warm and good sturdy walking shoes so you don't slip.
Waterproofs are an obvious 'must (though it has never rained on my three visits in July). The wind can be cold even in the summer (very few trees), especially near the sea. Take clothes you can layer on and off as necessary, and a warm hat (particularly if the wind makes your ears ache).
Photo Equipment: You will take many more photos than you thought you would!
Miscellaneous: Binoculars are an absolute must. There are so many birds ......and seals........and the other islands in the distance.........and the ships and boats! I forgot mine on my first visit, and bitterly regretted it.
good walking shoes are needed if you want to do any exploring.
A warm jumper and a water/windproof coat are needed as you as always close to the open sea and you are going to be out and about a lot... there is lots to do.
Photo Equipment: Lots of film, batteries are easy to buy.