If you are visiting Europe this summer, you probably want to pack light so that you don't have to drag around fifty pounds of luggage every time you hop on a train or plane to get from one country to the next. If you want to look chic while you are eating pizza in Rome, checking out the Louvre in Paris, or sipping wine in Barcelona, then you should probably give the cargo shorts, running shoes, and fanny packs a pass. You need vacation clothes that are lightweight, easy to store, and stylish. That way, you will be able to enjoy your trip without worrying about how you are going to get your enormous suitcase from one location to the next.
Choose wrinkle-resistant clothing. You can pack wrinkle-resistant clothing into very small spaces, then pull it out and expect it to look fresh. You will be able to save space in your luggage and avoid having to press clothes once you get to your destination. You do not even necessarily need to fold the clothes; instead, you can roll them and squeeze them in to your luggage tightly. You should also bring a stain-removal stick. These are compact and may save you the trouble of having to launder your clothing on vacation if you spill something.
One problem with visiting Europe in the summer is that the weather can vary wildly from one country to the next. It may be 90 degrees on the beaches of Barcelona, but only 60 degrees on the streets of Berlin. If you are doing a tour of Europe, your best bet is going to be to pack things that are easy to layer. Bring a pair of sweaters that you can easily slip in and out of. Cardigans are a great idea, and you can wear them over shirts or dresses. You may even want to bring a light jacket to wear at nights and on airplanes.
If you do not care about anything but comfort while you are traveling, then by all means, bring the cargo shorts, oversized old T-shirts, and New Balances. If you do not want to look like a popular stereotype of American tourists, then you should stick with long pants unless you are on a beach. For women, sun dresses can be an elegant and comfortable choice and ballet flats make a great substitute for sneakers. Men should consider fitted T-shirts or collared shirts and oxfords. Be aware that many old churches won't allow you in with bare shoulders or knees.
While you probably do want to bring enough clothing to fit in on a beach, in an art gallery, or at a nice restaurant, you don't want to fill your suitcase. Leave a little bit of room for souvenirs. Two pairs of pants, a dress, and three shirts will probably be enough for one week, if you don't mind wearing your shirts twice.