Renaissance fair garb

Items that are unsuitable for "everyday street wear" would be a costume in this instance.  

If you are a W-2 employee, none of your work-related expenses are deductible under federal law.  They may be deductible under state law, depending on your state and your other tax situations, so you can still list the expenses in TurboTax and they will flow to the state return if they are allowable in your state.

If you are an independent contractor, reporting your income and expenses on schedule, C, then the rules for deducting clothing, and uniforms are as follows:

You may deduct clothing or uniforms as a work related expense only if the clothing or uniform is distinctive, and not suitable for ordinary streetwear.  For example, a priest can deduct his collar, but not his black shirt and trousers. A Target employee could not deduct a red polo shirt or khaki trousers.  Without knowing the details, I suspect that most of your renaissance fair costume would be allowable under this rule.