According to IRS Publication 463, Travel, Entertainment, Gift, and Car Expenses, Chapter 1- Travel, "incidental expenses" are defined as:
- Fees and tips given to porters, baggage carriers, bellhops, hotel maids, stewards or stewardesses and others on ships, and hotel servants in foreign countries,
- Transportation between places of lodging or business and places where meals are taken, if suitable meals can be obtained at the temporary duty site, and
- Mailing costs associated with filing travel vouchers and payment of employer-sponsored charge card billings.
Incidental expenses do not include expenses for laundry, cleaning and pressing of clothing, lodging taxes, or the costs of telegrams or telephone calls.