Idiom: off the top of one's head

If you think of an idea 'off the top of your head', you thought of it easily, without trying hard.

How many US Presidents can you list? Just off the top of my head, I can think of Lincoln, Washington, Obama, Bush x2, Kennedy, Clinton, Roosevelt... (That means, I very quickly thought of these names. I didn't have to try to remember. I didn't do any research.)

Off the top of my head, it's difficult to think of another example. ^_^

This expression also suggests that your answer is not complete or perfect.
"Do you have any ideas for games for the party?"
"Well... off the top of my head, I could give you a couple of ideas. But I'll think about it some more."

"Off the top of my head, I think we have about twelve days until the party."

How about you? How long is it until Christmas? Imagine you are buying a present for your best friend - what kind of gift does he/she like? Please answer 'off the top of your head'. ^_^