Booth vendors often do a lot of driving. Between hunting for treasures, going back and forth to the booth, and running here and there for supplies, the miles really add up. At the end of the year, those miles are a tax deduction. If you wait til the end of the year to think about it, there's no way you'd be able to come close to being accurate.
The easiest thing is to stick a notebook in your car and make just a few notes anytime you drive somewhere on a booth related errand.
My notebooks only had 3 columns as shown in the picture below. You can total the mileage at the end of each month or at the end of the year.
Get started and let this be the year that you get a handle on keeping good records for your booth business!