Is this a thing where you are from?
I suggest here in Blighty, the waiters would be rather confused by such a request; not to mention something of a social faux pas.
In fact, it's not uncommon for the waiter to offer a box unprompted if you have a fair amount of leftover food.
Ah, this makes sense.
I recall eating in US restaurants and being given ridiculously large portions... something we half-joked - half-seriously suggested was down to the size of some of the patrons. Presumably is it instead the expectation that some of the food is taken home.
I'd imagine that it might differ based on where you are. Remember that the US is pretty close in size to the entirety of Western Europe. There are a lot of different places here.
If you're dining at a trendy spot in NYC or SF or LA, then you won't be taking leftovers home simply because portion sizes are small, or you're headed to a bar afterwards, etc. It's a different lifestyle.
But if you go out for dinner in most of the country where portions are supposed to be massive, it's pretty normal that after a round of appetizers, you won't be able to finish more than half your entrée. After eating, the server will ask if you want to "take it home" (sometimes using the phrase "doggie bag") and the answer is almost always "of course, it'll be great for lunch tomorrow", and they wrap it up for you. You're just driving straight home anyways.
If it's a business dinner or a fancy first date then maybe you wouldn't... but also maybe you still would. Leaving half of a delicious steak uneaten is pretty wasteful and can be kind of a bad look.
Feel free to browse the Cheesecake Factory calorie contents if you don't believe:
https://www.thecheesecakefactory.com/sites/default/files/202...
Their chicken katsu entrée, for example, is 2,520 calories. A regular teriyaki chicken plate is 1,550 calories. Of course you're taking it home.