So, lets think with portals.
Since it is possible to create infinite fall mechanism by placing two portals one over another it would be possible to successfully build perpetuum mobile device, thus achieve infinite source of free energy. I would use that to assume leadership position as worldwide energy supplier by delivering it for free, which would establish absolute governments and companies dependence from me. Having that I would order to stop all wars and conflicts, and become everyones dear king of the world.
But first, I would have some fun with it.
And you?