You can search
www.irs.gov for more information but it may take awhile to find what you are looking for. I recommend getting the book "J.K. Lassers Tax Guide". It comes out every year. The book tries to explain the tax laws in common language. Giving examples of what is allowed and what isn't allowed. Then it gives details about tax cases that went to court with how and why the court decided the way it did. And don't forget, it is deductible on next year's taxes.
As a general rule, anything that is
required by your employer as a condition for employment is deductible. But not everything. Some companies require pilots to have a watch, yet the IRS has made it clear that watches are "jewelry" and therefore not deductible.
If not required the IRS will look at: Is it a reasonable and usual expense for the job? Think flight bag or suitcase. Not required but certainly reasonable.
Third: Items that are used in both job related and personal uses will need to be pro rated and only that portion of job related use is allowed to be deducted. Think phone, computer, internet expenses.
Also, remember that just because someone tells you that they have deducted something in the past doesn't make it legal.
I could tell you that I drove 100 mph on the way home last night and didn't get in trouble, so it must be okay, right?