Bring more film than you think you will need since film is usually more expensive overseas. Always check the expiration of any film bought overseas.
Bring your passport and make sure it hasn't expired. Before departure, make a copy of your passport and airline tickets and keep in a separate place.
In Italy, you can also change money in the Italian Post Office. They often have better exchange rates and are open Saturday mornings.
I do not advise bringing traveler's checks. I have found that many restaurants and stores do not accept them because of currency fluctuation but you can exchange them at hotel front desks and banks.
Always bring comfortable, "already-broken in" footwear. Don't make the mistake of bringing brand new shoes! Never bring high heels - they will certainly get stuck in the cobblestones in the small villages. Remember, many of these European villages are very hilly with rocky textures.
Before I pack, I make a habit of checking the weather forecast of the country to which I will be traveling. Also, I bring a light jacket and a small umbrella.
For those die hard shoppers, always bring an extra, collapsible suitcase for those precious purchases. You don?™t want to break your new possessions by placing smashing them into your packed suitcase.
Expanding on the previous note, if you wish to purchase art/home decor while away, always bring the measurements of that area of your home (i.e. table measurements for tablecloths, bed measurements for linens, etc.)
Don't forget your laptop hardware, chargers (for cell phone, digital camera, etc.) and converters (hairdryer, electric shaver, etc.).