Hmm.
Just for one day, eh?
Off the top of my head I'd be a sorcerer or whatever you want to call it.
I'd teleport to D.C. and start grabbing politicians, generals, maybe even lobbyists and strategists if I have time, then popping them over to an empty dimension. Then I'd tell them they'd be there alone, cold, starving, slowly going mad forever, laugh in their faces and pop back without them to grab another.
Even if they don't remember it the next day knowing they went through that would warm my heart for years to come.