Apart from depreciation and deducting day-to-day business expenses, you can deduct any costs involved in travelling to your properties and also any costs involved in visiting potential properties. So you could be looking at beachfront properties in Los Angeles or some nice waterfront condos in Miami and put all your costs (including meals) through as legitimate real estate investor expense!
Should you attend any real estate conferences, exhibitions or training, these costs can be deducted too. It's very kind of your tenants to pay for your tax-free vacations. Just keep them realistic!
