Oh they're beautiful, thank you! But you really don't have to buy me flowers!
needn't have bought
I couldn't stand crowds, so I'm not looking forward to going to the concert next Friday.
can't
Today our offices aren't open, but I could give you an appointment for next Monday at ten o'clock.
can
Our neighbors with pets are disrepectful, and they have to pick up their dogs' waste so we don't step in it.
should/ought to
The bus got so hot that I felt that I can't breathe anymore.
couldn't
All of the tourists made an effort, but in the end only a few can make out what he was saying.
were able to
If you can't make the payment online you are able to do it in person during the office hours.
can (do it)
You don't have to smoke in the entrance of the building. Please go outside.
shouldn't/mustn't
I'd love to be able to help you with the move next week but I couldn't because I have to work.
can't
We always went to Indiana on holiday when I was a kid because we wouldn't afford to go on expensive trips.
couldn't