EasyRhino said:
Not that the IRS had not, traditionally, accepted casino win/loss as "proof" of losses to use as tax deductions. They have generally required that a fairly detailed log be kept of each session.
A recent court case out of san diego may have allowed win/losses. But it's still a great idea to keep a log if you have any significant chance of getting W-2Gs.
Per
http://www.irs.gov/taxtopics/tc419.html
"It is important to keep an accurate diary or similar record of your gambling winnings and losses. To deduct your losses, you must be able to provide receipts, tickets, statements or other records that show the amount of both your winnings and losses. Refer to Publication 529, Miscellaneous Deductions, for more information."
I take that to mean your written records should be pretty consistent with any win/loss statements and such. I suppose if you want to be a bit compulsive you could even keep parking receipts, dinner receipts and hotel receipts as proof you were in the area on the date your personal log and win/loss statements show.
It's like a business ... your books are the main thing but you should have receipts for most of your expenses. An auditor might give you a break and allow non receipted expenses on a few things if everything seems consistant, but not likely he'll allow $5,000 unreceipted for a business week in Vegas.