do one's bit

I asked her what put it into her head to do all this, and she said it was because one had to do one's bit somehow, and the harder the better, so that it sent one to bed tired enough to sleep.

How would it be to do one’s bit inside!

Those are the kind of things that make a man thank God for having volunteered to do one's 'bit' in that particular line of life in which he has been placed.