British to American terms I've picked up on:
wellies-> galoshes or rubber boots (sometimes called rubbers, but that gets you into condom territory - you might not want to go there)
stockings-> pantyhose or tights, but tights are more what little girls wear. (Stockings are like pantyhose, but you'll probably need garters to keep them up. If you're looking for stockings or socks in a US department store it will probably be labeled the hosiery department)
lorry -> truck
flat-> apartment (and here we have the first floor on the ground floor; anything below the ground is the basement, or if you're a realtor trying to make it sound better the "garden level")
I live in the midwestern part of the U.S. and here is one of the weirdest regional differences: In my state we say "drinking fountain", in a neighboring state they say "bubbler."
Many people from out of state played a children's game called "Duck, Duck, Goose," but we always played "Duck, Duck, Gray Duck." (We used to change it up and throw all kinds of colors in there. Much more fun that way.) And on a related note, I have no idea if I'm supposed to spell that "gray" or "grey."
In the morning we eat breakfast, at midday we eat lunch. In the evening we eat dinner or supper, but if you're having a big late breakfast it's brunch, and we sometimes eat a bigger (more formal meal) anytime on Sundays or on holidays (i.e. Sunday dinner or Christmas dinner). Sometimes you will go to a social event like a bridal/baby shower or a funeral/wedding and you'll have a "luncheon."
I usually use the word purse for my handbag, but then I agree with whoever said it was usually not something that goes over the shoulder and I agree with whoever said a pocketbook is more like a wallet.
When I was a kid we always said POP (or soda pop), but now many more people say soda. My cousins live in the south (FL) and they say soda, but not everything is Coke.
We have suckers, rarely lollipops. We have garage sales, yard sales or rummage sales, out east they have tag sales. I always try to say rummage sale, because you're not selling your garage, you're just having the sale in your garage.
My dad hates it when people pronounce route ("rowt") so it rhymes with boot (root), when they say "crick" instead of "creek" and some others.
OMGosh! Sorry to be such a windbag (what do you Brits call that?), but I've always thought the differences in language were interesting too.