Can you think about it just off the top of your head?
Tell me the first thing off the top of your head.
There is no other thing off the top of my head.
And sometimes right off the top of my head, he thought.
And those are just off the top of my head.
But off the top of my head, I don't think there will be many.
He can't come up with anyone else off the top of his head.
I really can't come up with a name off the top of my head.
However, this is just off the top of my head.
He won't know right off the top of his head.