First off, you're going to need a passport to get in and out of Ireland. Some border agents are sticklers about the amount of validity left on your passport, so if yours is set to expire in the next few months, it might be worth your while to get it renewed before you leave the U.S. People with U.S. passports don't need a visa to visit Ireland and can stay in the country for up to three months. Since you should never go anywhere without your passport, bring along a day pack or money belt in which you can store that most important document.
Ireland is a moderately cool country, with high temperatures only around 60 to 70 degrees Fahrenheit in summer. In winter, temperatures may hover around freezing at night. Pack clothing that you can layer for warmth when needed, including at least one warm sweater, a warm hat, a few pairs of long pants, and warm, moisture wicking socks. Irish people tend to wear dark colors, so you'll blend in by following suit and avoiding blue jeans or athletic gear. In general, people wear dark colored slacks, sweaters or button-down shirts for dining or going out to the pubs. Prepare for the inevitable "soft" rainy day by bringing a lightweight rain jacket and a pair of comfortable walking shoes that also keep out the rain. With wind gusts common on the coast, a solid raincoat is a better investment than a bulky umbrella. While it's always good to have at least one upscale outfit for dining out, Ireland is a relatively casual country, so you won't need lots of fancy jewelry or high-fashion attire.
Ireland has a wealth of ATM's that make getting cash easy -- just check with your bank before you leave to make sure they don't charge exorbitant fees for international withdrawals. If they do, plan to withdraw money just a few times, or exchange U.S. dollars for Euros at one of the many currency conversion booths in the cities and airports -- which also charge a fee. Traveler's checks are still accepted some places, though they're not common. If you plan to rent a car, your American driver's license is all you'll need, and expect to pay for local insurance coverage. If you're hoping to bring along any electrical items, you'll need an electrical transformer and a plug converter. Most of Europe runs on a 220-volt currency, including Ireland, so you'll risk frying your electrical devices if you don't have the necessary conversion tools. If you plan to bring your mobile phone, talk to your service provider before you go and sign up for an international plan -- else you'll face exorbitant international roaming charges.
In small towns and cities alike, the neighborhood pub is the center of the social scene. Walk into a pub when the workday is done and you're likely to find people dancing on the tables and musicians using fiddles, drums, penny whistles and voices to turn the room into a raucous song circle. In Dublin, the area around Temple Bar is the most lively; in smaller towns, find the neighborhood pub in the business district. You may not be able to fit your violin into your suitcase, but you'd do well to have a harmonica, flute or other small instrument in your possession so you can take part in the fun. If you don't play an instrument, bring a songbook of Irish tunes so you can sing along. Also consider other diversions, including books to read and journals to write in when the weather gets dark and stormy.