Didn't need to vs Needn't have

Yesterday was Saturday, so we .....

My mother gave me some money so I .................................

I knew the grammar very well so I....

It wasn't sunny so I _______________ sunglasses

We ................ because we ordered takeaway food.

Sandra ________ the clothes because Sue had already done that.

You.............................. I ate on the plane.

It's not raining. You........................ an umbrella.

The plane was late. I.................. to the airport so early.

Thanks, but I already have an iphone. You.....

The word 'let' in the title is used to express ....

The word 'should' in the lyric is used to express ....

I ________ last night as I knew you were going to have dinner with them.

The previous owners had already decorated the flat, so we______ it ourselves.

I didn't realize it was free to enter the museum so I ...............

Service was included in the bill, so you________ the waiter. It was a waste of money.