One of the biggest problems for me before I left the States for Italy, was what on earth to pack for a 2 month excursion studying fashion in a city I've never been to. Every fashion student knows that one must have the feel of the city to understand what to pack for it, so I was going into this journey completely blind. After my lovely stay in Florence, I have a few words of wisdom for future fashionista's on their way to Europe, and more specifically Italy in the summer.
1.) A large, light-weight scarf. This came in handy every time I wanted to visit an old cathedral, friar, or Duomo. The Italians (and some places in France I found as well) are very serious about maintaining proper dress, so shoulders must always be covered. Instead of wearing long sleeves while you are hiking through different cities, wear what you'd like and cover your shoulders with a scarf when entering sacred places. When you aren't using your scarf, tie it around your bag as a colorful accessory. Just remember, that often times (particularly St. Peter's Basilica) your shorts and dresses need to be at least knee length -- guys, too!
2.) One maxi-dress. They were quite the rage when I was in Italy, plus they are nice if it happens to be a chilly night.
3.) One good pair of sunglasses. Seriously, you won't regret them. It rained only twice the entire time I lived in Florence.
4.) A pair of wedges. The Italian women, and actually most European women I found, frequently wear heels. I hail from Indiana, where this is very much the opposite of the norm. Now, remind yourself that many of the roads in Italy and Europe are cobblestone, so if you have not been wearing heels since you were 5 years old, you most likely will roll your ankle attempting to navigate the alleyways, and in the very least you will find you are staring at the road rather than taking in the beautiful sites. So here is a great compromise: wear wedges! The footing is more stable than a thin heel, but will give you the same stylish feel.
5.) One trusty black dress for going out at night. The Italians are all about night life, as much as they are about getting dressed up. Looks are very important to their culture, but instead of bringing 10 different dresses, bring a few trusty ones, and bring (or buy at the markets!) jewelry to switch up your looks instead.
For any of you lucky enough to be heading abroad I hope this helps. Maybe a post on what NOT to pack is in the works... because you are going to need all the suitcase you can spare to bring home your treasures from your travels.