a car's boot is called the "trunk" and a car's bonnet is called the "hood".
petrol is called gas, which is short for gasoline.
chips are called "French fries" and crisps are called "chips".
fizzy drinks like Coca Cola and Sprite are called "soda" in some places, "pop" in others and "tonic" in Boston.
a laundrette is called a laundromat.
the servers at restaurants and pubs typically receive a 20% gratuity (tip) from the consumer (you) at the end of the meal. It's left on the table as one leaves, handed directly to the waiter or waitress in dodgy places, or added to the credit card bill. It is not mandatory, but it's absence is considered very rude unless the service was truly bad.
motorways are called Interstates
driving directions are given according to the compass heading on a road or motorway and for distances expressed in travel time. They would say that Cambridge is an hour and a half north of London on the M11.
a lorry is a "truck" and a coach is a "bus"
their Undergrounds go by different names depending on the city. In Washington, D.C., it's the Metro. In Boston it's the "T". In New York, it's the subway. In Chicago, it's the "El", but subway seems to be the most universally recognized term.
things tend to be less expensive than in the U.K.
few people understand cricket or rugby
the Democratic Party is more like Labor and the Republican Party is more like the Tories
people in the city tend to be Democrats and people in the countryside tend to be Republicans.
they usually can't tell that your from England, Scotland, Wales or North Ireland by your accent, let alone Cornwall, Yorkshire or any other smaller part of the U.K.
they usually think you're smart or at least interesting because of your "English Accent".
they might say "Excuse me?" or "Please?" with a quizzical brow if they don't understand what you said and want you to repeat it.
they are usually kind, patient and helpful to Brits if you ask for help with a smile.