I've never really thought about it, as I have always known I never would be rich.
However, let's give it a try.
Playing that grand piano would be high on my list. Being able to go to the theatre or a concert whenever I wanted to, irrespective of what the tickets cost comes next.
Buying any book I wanted, again without having to think of the cost,
Being able to phone Caritas and say they could fetch 20 injured, reconvalecent children from Ukraine and either their mother or grandmother here for a fortnight's holiday, and that I would foot the bill.