Rain Gear, Derry
Wherever you travel in Ireland make sure you pack the right clothes. When travelling in the summer don't just pack shorts and t-shirts - the weather can change often and quickly! Waterproofs always come in handy. Some Derry people might walk around in shorts/skirts and t-shirts in all temperatures, but you might find it way too cold :o) And don't forget your walking boots, Ireland is perfect for hiking.
Camping/Beach/Outdoor Gear: If you're brave you can bring your swimming trunks for a dip in Lough Swilly across the border in Inishowen/Donegal. Be warned though - it's bloody freezing even on a hot summer's day!!!
Miscellaneous: If you intend to go clubbing then be warned that most clubs won't let you in wearing sneakers or sport labels. Bring your good clubbing shoes/clothes if you want to hit the tiles.