The correct answer is a night on the town.
When Doolittle meets Higgins and Pickering, he actually wants to sell his daughter to him for five pounds. He thinks she will have a better life there and he will spend that money "wisely." This are his actual words:
"Just one good spree for myself and the missus, giving pleasure to ourselves and employment to others, and satisfaction to you to think it's not been throwed away. You couldn't spend it better."