Kit fee is just an amateur makeup artist's way of charging you a fee because your work is not worth trading for. It's a way for them to try and lessen the blow by making it sound like you are getting a wholesale rate. Ignore what people label in front of the word fee. Just read it as a fee. It’s simple as that. What it means is that your work or project is not beneficial enough for them to do it without charging that fee. If it makes you feel better, consider it a discounted day rate. If you want it to make you feel worse, consider it a "I'm not good enough" surcharge.
Every collaborator in a TF shoot or test has cost but there is no such thing as a photographer kit fee to cover battery cost, electricity cost, or pro-rated depreciation cost on equipment. Models don't charge kit fees for gym memberships or pimple removal creme. The origin of kit fees come from film productions where MUA may have to use expensive disposables such as wigs and other special effects supplies. The cost for these supplies are reimbursements and not viewed as taxable income. There are valid kit fees in film production but it's not used in still photography testing. Professional MUA charge a fee.