OFF  THE TOP OF MY HEAD      

 If you say something off the top of your head, you say it without thinking about it much before you speak, especially because you do not have enough time.

“Do you know how many people attended the meeting yesterday? ” “Hmm… OFF  THE TOP OF MY HEAD, I’d say around fifty, but I’ll check” “Do you know any nice restaurants nearby?” “OFF  THE TOP OF MY HEAD, the only place I can think of is a nice Italian place round the corner”

MY GO-TO…

It is the thing you always choose because you love it or trust it.

“This is my go-to restaurant. Ialways come here. ” “This is my go-to dictionary. I use it every time.”

COME IN HANDY

It means that something is useful

“A pair of jeans will also come in handy.” “I always keep an umbrella on me. It comes in handy in London ”

ON AND OFF

It is something that starts and stops repeatedly, with breaks.

“I have been dating  him for three years  on and off.” “I have been learning English for seven years on and off.”