Gambling losses can be deducted but only to the extent of your winnings.
Keep all your race track losing tickets. Keeping a dated program helps. Keep all your losing scratch off and lottery tickets.
As far as casinos go, most will supply you with a win/loss statement if you ask for it.
Add it all up and pay taxes on the rest.

If you plan any trips to any casinos before the end of the year, make sure you use your comp card.