1: Gambling losses not in excess of gambling winnings can be deducted on Schedule A, line 28. See Pub 17 (p 201). Line 28 catches lots of deductions, and gambling losses are one of them. See Schedule A instructions.
2: If the Mississippi state tax withheld was an income tax (which I assume it was), then it goes on Schedule A, line 5a. In the unlikely event it was not a state or local tax on income, but some sort of excise on gambling, then it may be deductible on line 8 as another deductible tax. It probably is not a personal property tax, which is generally levied against the value of things like cars and other movable property but not on receipts of cash; line 7 probably is not appropriate. The most likely result, without researching Mississippi SALT, is that it was an income tax. See Sched A Instructions for more on the differences between the types of taxes paid.
Just to be clear, these statements hold if you are not engaging in poker as a profession. If you are engaging in poker as a business, which can be difficult to establish in the IRS' eyes, then you would use Schedule C and also report business and travel expenses. But the IRS is aware that people want to reduce their gambling income by the cost of hotels and flights to casinos, so it's a relatively high hurdle to be considered a professional poker player.