Pack your passport, but before you put it in your non-checked luggage, check that it's not set to expire within three months of the end of your visit. All U.S. citizens need a valid passport to enter Belgium and get back into the United States, but you won't need a visa if you're staying less than 90 days.
Check the weather conditions for the time of your stay. Like most of Northern Europe, winters in Belgium are fairly mild and wet, with temperatures around 40 degrees Fahrenheit during the day and lows in the 30s. Summers are warm but mild, with high temperatures averaging around 70 degrees.
Pack conservative, dark-colored clothing that will fit in with the dress customs of residents of the country. In general, Europeans don't favor shorts and T-shirts or brightly colored clothing, but instead go for darker, lightweight slacks or skirts and button-down shirts or blouses. In winter, wool is a good choice for materials because the weather tends to be damp and cool. In summer, choose cotton or linen and pack layers such as a sweater -- as opposed to a sweatshirt -- and a lightweight as well as a heavy scarf.
Get a pair of sturdy boots that will protect your feet in the rain but don't look like rain boots. Think leather zip-up boots as opposed to hiking or outdoor gear; Belgians don't tend to wear outdoor gear unless they're spending time in the countryside. On the flip side of that, avoid really high heels because some of the streets in cities such as Brussels and Brugge are still cobblestone.
Pack a lightweight raincoat. If you have a pea coat, trench coat or something similar, pack that as opposed to a hiker-style raincoat. An umbrella is also nice to have, though you can also buy one there if you need it or borrow one from your hotel.
Take along any essential beauty items, such as your favorite shampoo, since you may not be able to get the same brands in Belgium. Also keep in mind that Belgium's electrical outlets operate on 230 volts; much more than the United States' 120 volts. Check with your hotel to find out whether they have hair dryers or voltage converters and plug adapters that you are able to use. If not, consider purchasing a converter for your electronics when you arrive to keep from burning them out because of voltage that is too high. Some electronics, such as mobile phones, are designed to work with multiple voltages, but you could need a plug adapter to plug them in. In any case, check your device's user guide before charging anything abroad.
Pack a phrasebook that can help you communicate when you are sightseeing and traveling in Belgium. Many Europeans speak English, but not all do. The official languages of Belgium are French, German and Dutch, but many people speak Flemish as well. In Brussels, expect people to speak either French or Dutch.
