A piece of cake
A task or activity that is easy to complete
Get the green light
To get permission to do something
monkey see, monkey do
silly/unintelligent people tend to copy each other's actions
Raining cats and dogs
Raining very heavily
Money doesn't grow on trees
money is limited
A couch potato
A lazy person who watches too much television
Once in a blue moon
Very rarely
nest egg
money saved for the future
Bone Dry
Completely dry, totally without moisture
Born with a silver spoon in your mouth
born into a wealthy family
cool as a cucumber
very relaxed
To pass with flying colours
To pass something with a high score
kill two birds with one stone
get two things done at once
To be on thin ice
To be in a risky situation
Dime a dozen
something is easy to get or common.
use your noodle
use your brain
once in a blue moon
very rarely
hold your horses
wait and be patient
On cloud nine
Very happy
Pour money down the drain
waste money
Two peas in a pod
Nearly identical, very similar
A golden opportunity
A very good chance to achieve something
Let the cat out of the bag
A secret that was supposed to be kept quiet that was told
Right as Rain
Absolutely correct
Bring home the bacon
to earn a salary (which enables you to buy bacon)