I posted this years ago.  In Maryland we have what is called the dirty shoe rule.  With the Preakness held here we have a couple of race tracks.  People who lose the race just drop the tickets on the floor / ground.  Others would scoop them up and claim them as losses.  The state says that any ticket that looked like it was on the ground would not be counted towards gambling losses.  The best way at casinos is to get a printout from the casino rewards card that will show the amount of money you spent, assuming all of it was used with the card.  The problem there is the card printout would show all winnings, not just the W-2G reported winnings.