Keep An Eye On:
Can you keep an eye on my baby brother while I talk on the phone?
Keep somebody up to date about something.
Keep me posted and tell me if you get accepted to that university!
Keep your chin up:
Stay positive when things get difficult.
Keep your chin up. Things will get better.
Kick The Bucket:
Don’t kick the bucket! I need you around!
Kick the Can Down the Road:
To delay a decision hoping that it will disappear or that someone else will have to deal with it.
The politicians didn't create the important health care law because it would have been unpopular. They kicked the can down the road and future generations will have to face the difficult decision.
Knock On Wood:
Literally knocking on wood (or other hard surface) for good luck.
When my friend went in for a university interview I said, “Knock on wood!”