Second jobs can lead to tax deductions. Actually, in some cases, you can claim expenses on your US income tax for first or second jobs. Via TaxMama, here’s a great post about tax deductions for second jobs.
In Canada, some people are entitled to deduct employment expenses, too. This is possibly the case in other countries. Regardless of whether you have just one job or a second job, you should look into whether or not you can claim employment expenses you incur through your work. If your employer doesn’t reimburse all your expenses (such as when you drive on errands or buy supplies), you might be allowed a tax deduction.
Original link was to http://www.asktaxmama.com/podcast/index.php?id=376.