I’d find out about betting opportunities all around the world, so that I could place a big bet when I woke up at 5am, and collect my payoff by 6am, so that I could have all day to spend it.
Since I’d wake up ‘tomorrow’ weighing the same as I do today, I’d eat whatever I damned well pleased. I’d be eating at different restaurants every day - Salvadoran for lunch, Burmese for dinner, you get the idea.
I would explore the D.C. area, where I live, in great detail. I’d do the same with NYC, since it’s only three hours away by train, is a fascinating city, and is absolutely tops when it comes to variety of restaurants.
I’d travel as far as I could in a day (and still have time to enjoy my destination for a few hours) on a regular basis, to all sorts of different locations. I’d do a lot of hiking in the Rockies, and a lot of bicycling in all sorts of different places. (Pity I’d never be in any better shape than I am right now, though.) Now that the Concorde is history, I guess I’d only get to spend late evenings in Europe. But I’d travel there comfortably.
One issue nobody has raised so far is having this happen while being married. If you’re having this happen to you, but your spouse, like everyone else, thinks she’s experiencing this day for the first time, what do you do? Do you let her go off to work none the wiser, while you go off and play on your own? Or do you try to convince her that she needs to call in sick today, because you just won ten zillion euros on a longshot bet on the horses at 6am, for the googolplex’th time, and you’ve chartered a private flight for St. Maarten?
I think I’d probably do a bit of both, over time. But ISTM that being in a ‘Groundhog Day’ situation would be best if you’re either single or in a flexible relationship, i.e. one where your SO isn’t panicked if they don’t see or hear from you in a typical day.