"Unreliable weather" London Packing List Tip by bzh

Luggage and bags: Suitcases or backpack, it doesn't make a difference really. However, if you have to travel by tube with your luggage, make sure you have something you can carry up and down stairs without too much trouble.

Clothing/Shoes/Weather Gear: Remember that there is no guarantee whatsoever that the weather in London will be nice, whatever the time of the year. Make sure you have one or two warm jumpers, a raincoat and an umbrella.
A good pair of shoes is also essential as the best way to visit London is to walk.

Toiletries and Medical Supplies: The usual things you would take anywhere in Europe. If need be, you can find everything at stores like Boots.

Photo Equipment: Take a wide angle lens for city perspectives and a telephoto for architectural details. A tripod or mini-tripod will enable you to take striking night shots of the city.
In terms of film, good, fine-grained 100 ASA will give you the best results. Don't hesitate to pack a few fast films as well, such as 400 ASA in case the weather is overcast. Black and white film can produce dramatic pictures in the city.
Make sure you keep your equipment in a bag that can stand rain and that you can carry in front of you as pick-pockets are quite common in the most popular spots.