Bring rain gear. I hitchhiked through Ireland in June a few years ago. The weather forecasts are pretty useless for Ireland.
I would bring "Performance century cycling shorts", they are very comfortable and on sale for $29 right now.
http://www.performancebike.com/shop/...tegory_ID=1120
It's a great country and you will love it.
There seemed to be a bike shop in most towns.