Don't forget, the British drive on the road and walk on the pavement, while Americans drive on the pavement and walk on the sidewalk.
Some words would mark you as an American in Britain, irrespective of your accent. For example, the British never, never, say "in back of." Something in the rear of another thing is "behind" it. Which is illogical, since in Britain you speak of something being "in front of," so why not "in back of?" To be consistent, the British should speak of something being either behind or "before," which is an archaic or poetic construction (e.g. "putting the cart before the horse.")
As long-time forum members know, I have a passion for the English language, and especially semantics. Many English usages that sound strange to Britons were common in Britain a century or two ago, and in many instances it is British English that has changed, as in "in back of."
Interestingly, even the "generic" (i.e. mid-western) American accent is quite similar to the way people spoke in England only a little over a century ago. There are some ancient wax-cylinder recordings of Prime Minister William Gladstone, made around the beginning of the 20th Century, and he sounds very similar to someone from, say, Illinois.