First off, buy a castle, or if I don't find one I like, have one built, and then buy up all the land around it and plant a huge great forest around it,
Then buy huge amounts of military hardware, guns, tanks, e.t.c., not to invade anywhere, just cos I'm fascinated by all that stuff.
Then develop my own Iron man suit/Space Marine power armour, for the awesomeness value,
Then probably walk around the streets of the major cities in the UK, donating to the homeless, to help them restart their lives.
Pile large amounts of money into hydrogen fuel developement.
Then put together an enormous space exploration programme, to try and find a habitable planet for humanity to start occupying. That's the thing I don't understand about the current state of space exploration, i.e. non-existant. The human race is at 7 billion and counting, and the planet will not be able to sustain it for much longer for the same reason you can't build a skyscraper out of bricks. We either need some enforced sterilisation, or need to start expanding out into the galaxy before the planet collapses from underneath us.