I've already covered what you should pack for a semester in Italy, but there a few common items that some students think to bring that are actually unnecessary. Save yourself the hassle of bringing these items and leave room in your luggage for souvenirs or whatever else you'll want to bring home after four months of travels!
Full-sized or Large Toiletry Bottles
It's nice to have just one regular sized bottle each of shampoo, conditioner, and body wash at home. Though when you're studying abroad, even though you have a home base, you'll likely be traveling most weekends. It's easier to have a few travel sized bottles that you can use and also take with you on trips. If you run out, you can always buy more. When I went abroad I made the mistake of stocking up on a large sized body wash, etc. and had over 10 pounds of liquids in my checked bag - these took up room, but more importantly, made my suitcase get closer to the airline's standard weight limit.
If you're living in Italy and traveling throughout Europe, you'll mostly just need this converter. You can get singles from Target for about $3-4. (If you're going to the UK, you'll need this one). Many people buy the world-wide converters that can be $30-40. Unless you're traveling to other regions after your study abroad, save yourself the money by just getting a Europe converter.
Sheets and Bedding
Your host family/dorm/apartment should have sheets for you. If you're unsure for some reason, get in touch with your host family or the study abroad staff and ask. In most cases, hostels will have full bedding. I've stayed in both private hostels and cheap dorm-style hostels all around Europe, and every time my hostel has had clean sheets and towels. Definitely check up on this beforehand by doing your research on Hostelworld or reading reviews.
Chances are your dorm/apartment/house back on campus is decorated with your own style and flair. When you get to Italy, you'll already have furniture and decorations, and bringing your own is just unnecessary. Plus, the rooms tend to be pretty small and you won't have much room anyways!
A Ton of DVDs
Netflix and Hulu technically aren't available in Europe yet. However, if you use this handy trick you'll be able to access those and similar sites. (Note: works on laptop/desktop, not mobile!) Hopefully you'll be spending a majority of your time out exploring and traveling, though there may come a time when you just want to relax with a show. Getting your TV and movie fix online saves you room and leaves less opportunity for your DVDs to get damaged.