Hi,
Situation 1:
You come into a restaurant that offers 'take out food'. (for example "Denys").
A waiter comes up to you to seat you at a table.
You need to say that you want 'take out food'.
What would you say in this situation?
When I order take-out food, I normally do it by telephoning the restaurant from my home. Then they deliver it to me.
Occasionally, I order it by phone and then go and pick it up. I order by phone so that I don't have to wait when I arrive in the restaurant. In such restaurants, there is normally a counter clearly marked as the place where I can pick it up. So, I never talk to a waiter.
Situation 2:
You make your order in McDonald's.
Making your offer you need to say that you want to take it out.
If I'm in my car, I just stop at the special 'drive-thru' window.
If I go inside, I just tell the person taking the order 'It's to go, please'. McDonald's doesn't have waiters.
Situation 3:
You suggest your friends take 'take out food'.
Is it correct to say "Let's have takeout today."?
Yes, that's what I might say. But again, I'd order it by phone and have it delivered.
Best wishes, Clive