I can't finish this.
I can't eat another bite.
I really like dessert, but I can't eat it now, can I get it to go?
Do you have a doggie bag?
Do you have something I can put this into?
Could you put the leftovers in something, so I can take them home.
A: I can't eat all of this, can you wrap up what's left to go?
B: Certainly, I'll take care of that.