Average high temperatures in London and Paris for May are around 65 degrees Fahrenheit, with lows in the mid-40s for London and mid-50s for Paris. Accordingly, bring a light jacket or sweater. It will probably rain more in London than Paris, but chances are good that you'll need a raincoat in both cities.
Sightseeing in Paris and London requires a lot of walking. Many attractions, such as the Eiffel Tower or Parliament, are best viewed on foot. Even if you are on a bus tour, you'll probably be walking around museums, churches and castles. Pack at least one pair of comfortable walking shoes. Also include a pair of dress shoes for more formal evening wear.
Unless you plan to work out while you are in Paris or London, leave athletic clothes at home. You will stand out as a tourist in fluorescent Nike shoes, jeans with holes and T-shirts with advertising. Neat blue jeans are accepted casual daytime wear, but they may be out of place in restaurants. However, you can wear a pair of black trousers anywhere. Add a selection of basic, solid-color short and long-sleeved shirts, and you will fit right in.
If you have a big, formal evening planned, like a night at the Paris Opera, take one spectacular outfit for that occasion. Otherwise, women should bring a versatile black dress or skirt for evening wear. A silk shirt is appropriate, too. Men should bring a dress shirt and a sport coat, but ties are not required in most venues.
Use accessories to tie outfits together. For instance, a colorful silk scarf can double as an evening wrap. For a riverboat trip on the Seine or the Thames, a wool scarf can add a little warmth, as well as color. A simple string of faux pearls will give women's outfits a touch of class. Men can add a soft felt fedora to their suitcase to blend in while people-watching.
