The BigStock blog has a great visual article showing some key differences. Here's some of our favorites!
Trainer:
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BRACES:
CHIPS:
(also, expect funny looks if you eat yours with mayo in the US, especially if you whip a tube out on a picnic)
Read the full article here.
Oh, and needless to say, order your prepaid USA SIM card before you leave the UK from Telaway!