Here is a list beginning with what I found to be the most useful.

• Most resturants will not have ice, not even as an option. However, if you do ask for it, they will know you are American--which is not always what you want. I suggest that unless it is offered to you, do not ask for it.
• American sodas are sold in Britain, (i.e. Coca-Cola, Pepsi) but they do taste differently. I highly recommend drinking only Fanta. It tastes amazing over there, I will not even drink it here anymore. Also, it is somehow much less fattening. I would drink two or three a day and I lost weight!
• Most of the words used to describe the railroad and subway are the secondary terms in America. The British say railway and metro, for instance. When in the metro station, you will hear "Mind the Gap" and see it written on the floor everywhere. That is because there is a space between the rail cars and the pavement. "Mind the Gap" is a popular saying for souviners in London.
• Floors of buildings are numbered differently. What Americans call the "first floor", the British call the "ground floor." Therefore, if you live on the American second floor, the British would say you were on the first floor.
• Fish and chips. This is something you want to eat. British food is pretty different compared to American food, even McDonald's is not really the same. However, they know how to make fish. In Cambridge, the best place to go is the Eagle Pub, also known as the RAF bar. It is an amazing place.
• Pub = Bar
• Car park = parking lot
• cash machine = ATM
• flat = apartment