All travel expenses which are ordinary and necessary to the production of income are deductible
. IRC 162(a)(2). Meals and entertainment expenses are generally not deductible, unless there is a bona fide business need for the expense. IRS
first-line auditors are interested in documentary evidence (e.g., logs, receipts, etc.). If you have documents proving that you paid the expense and describing the purpose, then the auditor will allow the deduction
-- otherwise not. It's actually a lot more cut and dried then you may think. Auditors are not permitted to act as a judge. They either find that a deduction is documented and satisfies the requirement of ordinary and necessary expense -- or, it doesn't.
If you stick with the cost of travel (air fare, taxi, rental car, parking, hotel), and stay away from charging meals and entertainment, and you document your expenses, then you will survive an audit. Simple as that.
Hope this helps.