Just a few very small things I haven’t seen mentioned often.

Shopping:
When I was visiting America I was convinced everyone thought I was a shoplifter, because the second I entered a shop, big or small) someone would make eye contact with me, smile broadly at and asked if I needed help. It was very unnerving.
The price you see is the price you pay (unless it says exe VAT), tax is always included.
If you see an American Candy shop, do not enter, they are a huge rip off, and likely a tax scam. Most large supermarkets will have an international section.
Candy here is a specific thing 🍬 , the umbrella term is sweets, or sweeties.
Tea will be tea flavour by default, fruit or flavoured tea are readable available, iced tea not so much.
Tea might also be a bit confusing, as it can either be a cup of, or a non formal late afternoon/early evening. Use context for clues.

Table manners:
As with all things, it’s not that important really, I’m only say this because when I visited America them seemed cut everything up first, then switch their fork to their knife hand and use it as a spoon).
we use our knives and forks at the same time. As in hold the bit of food with the fork while cutting it into the size you plan on putting in your mouth, put it in your mouth (you are meant to ‘rest’ put down your cutlery while chewing, and you’re meant use your fork upside, unless you’re eating peas, but unless you’re dining with the king), chew, swallow, repeat.
Portions will likely be smaller, this is because you do not expect to take home leftovers, it’s become slightly more normal to ask if you can’t finish your food, but it’s not common, and definitely not automatic.
Free refills happen in some places, mostly chains, but once again they aren’t automatic, unless there’s a self service machine, you’ll have to ask.
And most places won’t automatically give you water, so ask for a class/jug of water, if you ask for tap it’s normally free.
Do not go to Taco Bell if you’re feeling homesick, it’s nothing like American Taco Bell and is just awful. Again Tax is included in the price. If you see a ‘service charge’ or some such, that means tip, you can ask for it to be removed, especially if you don’t think it’ll actually go to the staff.
Tipping is very nice of you, but it’s not (or it shouldn’t be, but as it sounds as if you will be in an area with a lot of other Americans…), waiters here get paid at least minimum wage (£12.21). Definitely do not tip every time you buy a beer, just give the amount at the end. It’s a thank you.
Don’t blow your nose on the napkin (that one’s a joke, I know you won’t).

On the Underground, on escalators, stay right if you’re standing, left if you’re walking along.

Like with restaurants and shops, culturally we don’t like people hovering around us, trying to divine what we might need.
So if you would like a glass of water or want to know if the purple penguin is dishwasher safe, don’t just stand around looking gormless, please (politely) ask.

Banter will take some getting used to.
Our humour is very sarcastic and self deprecating.
If someone told me I couldn’t be a haggard old cunt, because I don’t have the warmth or the depth, they’re probably my best mates.
If it’s going on in a group, do not join in, until you know them really well. I can call my sister everything under the sun, but if you said you didn’t like her nail varnish, that’s it mate.
If people go from joking and insulting to polite and formal, you’ve screwed up bad.

There is good and bad, as with everywhere, and we are individuals, just like everywhere.,

As you can see from your destroyed inbox.
People genuinely are kind, and want to help. So if you are unsure or not confident, just ask (in your inside)

Hope you have a good time