For a start, floating might be really fun, but what else might you get up to?
I’ll play but what are the rules here? Can I move objects? Do people hear/see me? Ooh, can I possess people?
Let’s suppose basic ghostly/poltergeist capacities, so nothing on the level of a great spirit or deity, in which case basically yes to what you mention (and in similar ways, so the whole hearing/seeing would be something you could flip on/off, make a case by case to mess with folks, etc.).
Haunt some of the powerful but evil people in the world and see what I can change. Let’s see how effective a dictator like Kim Jong Il can be with a ghost all up in their business.
If I have poltergeist abilities then I suppose just straight up assassinating people would be possible. After all, if you can shove a book off the shelf or flip a light switch then breaking a few tiny blood vessels in someone’s brain to give them a stroke is going to be easy. Not that killing other people would be easy, but maybe as a ghost I’d have a different perspective on death.
Spend the first hours exploring my limits… how high can I float, how fast, walk through walls etc. Then go places I shouldn’t be… listen in on stuff. With all the UFO/alien stuff lately I’d go to Area51 and snoop around.