Whether you're headed to London for business or you're just hoping to be one of the many tourists tottering around Piccadilly Circus, one of the first things you'll need to do is pack your suitcase. People in Great Britain tend to dress more conservatively and in darker colors than you may be used to in the United States -- and the September days tend to be darker too. If you're used to the blazing sun, be prepared for wetter, cloudier days than what you see back home.
You can get nearly anything you'll need when you're in London -- you could even manage to get a forgotten prescription in a pinch. However, the only thing you can't live without is your passport. Unlike other countries, your passport won't need to have a certain number of months of validity in order to be admitted to the United Kingdom, according to the U.S. Department of State. However, yours should at least be valid throughout the duration of your trip. For tourism and short-term business travelers, you won't need a visa -- though if you have special circumstances, check with the U.K. Border Services Agency before purchasing your airline ticket.
Check the Weather
In general, September in London may include a bit of sunshine, or a whole lot of rain. The best thing to do before you go is to check the forecast. On average, highs can be in the upper 60 degrees Fahrenheit -- about 20 degrees Celsius -- with average lows in the mid-50s, or about 13 degrees Celsius. September is not the wettest month of the year, but you should also expect some rain. To deal with the showers, you'll need a light rain coat as well as a compact umbrella or "brolly," as they're called in London. Rain boots, called "Wellies," wouldn't hurt either, but they may take up more room than you have -- especially if you're only taking a carry-on bag. A better option may be a more stylish, comfortable pair of leather boots that you can also use for going out to dinner as well as walking around town. If you decide on the leather, spray them with waterproofing solution before you depart.
Dress In Layers
With temperatures that are less-than-tropical, packing layers is going to be key for a trip to London in autumn. A warm, lightweight scarf can dress up an outfit and stashes well in a day bag. Likewise, a light sweater or cardigan should be a daily addition to your purse or day bag. Pack a mix of long-sleeved shirts or blouses, and slacks. To add extra warmth without adding bulk to your suitcase, pack a couple pairs of wool tights or silk long underwear.
With your nose inside a map of the London Underground, you may not be able to hide the fact that you're a tourist, but that doesn't mean you shouldn't make at least a little effort to blend in. In general, Londoners skip the white tennis shoes, jeans, and sporty-style jackets and clothing. Instead of a rain jacket made from synthetic fiber, for example, you may opt for a wool pea coat. Instead of the white tennis shoes, you might opt for a darker colored pair of soccer shoes for walking around. Instead of the ball cap, choose a wool bowler or fedora.
Using Your Electronics
If you plan to use gadgets such as a hair straightener or a laptop, you'll need to bring along a plug adapter or a voltage converter. The United Kingdom runs on 220 voltage -- much higher than the 120 volts used in the United States. Some of your devices may be "dual-voltage," meaning they'll run fine on either voltage with the addition of a device that changes the shape of the plug -- called an adapter. Other devices, meanwhile, will require that voltage converter, which will reduce the voltage coming out from the plug. Mobile phones and laptops are typically dual-voltage; other electronics are often not. Check the label on any devices you want to use to see what you might need, then purchase the right converter/adapter. You may also simply check with your hotel to find out whether those items are provided.