Pennyless Joe, the broke archeologist, finds an old pawn shop selling something curious. A ceramic vial labeled "Groundhog Day Potion". It's a bargain for $1.99. (He buys it, because he is not quite that broke).
Pennyless Joe is very intelligent (though not financially savvy) and well versed in archeology and alchemy.
After buying and studying the potion sample, he learns that the potion is real, still potent and allows the imbiber to "Groundhog" - relive an entire day with full memory of what happened on the first iteration of that day, but you only relive the day a single time.
He also knows there is no way to duplicate the potion, because it requires a long-extinct herb and the magic in the potion will be spent at the start of the replayed-upon day.
But alas, by breaking the seal, the millennia old potion begins to lose potency. Pennyless Joe's alchemical knowledge tells him that the potion will only be useful by December 24th of 2016.
So Penniless Joe wants to use the potion to reverse his wealth predicament, and make the most cash out of this single day.
what should his winning strategy be for this one day, to get really rich?
This does not break or invalidate any answer already posted at the time of this edit so:
Penniless Joe does not have much money on him after buying the $1.99 potion. He does have an income, but it barely meets his monthly expenses.
You can make any assumptions about his credit rating or any other ease/hardness of obtaining credit.
Also keep in mind that he has one year to use the potion.
P.S.: please do not answer with some potion-duplicating infinite loophole. It is intended to be a single-use artifact.