Pay off my mortgage but I would buy properties in the cities I would like to be able to visit often. Sydney, Melbourne, London, to name a few (more would follow).
I would also buy each of my children a home.
I would really like to make a difference for people I don’t know too. So I would definitely want to instigate some charitable projects. Not just give to charity, but be involved and create change in a targeted way. For instance, scholarships for Indigenous kids here in a range of fields. Put in place programs to help refugees transition and settle into their new home. Work with families who are struggling across a range of situations. Try to put in place initiatives to generate more community connectedness. I think many of the problems we have in society are about how disconnected our communities are becoming. Work with the homeless to try to ensure people in my country at least, have a roof over their heads and help to get out of the situation they are in. Places to go and shower and get ready for an interview for instance. A place to access email so you can actively seek work/shelter.
And probably a hundred million other things…