If you will be crossing state lines, check to see how your neighboring states collect their state sales tax.
Also check your state's DOT laws and requirements.
Your local Chamber of Commerce should have some information available to help you, and may recommend a business mentor as well.
Get permission from the track ( or tracks) you wish to vend at first.
You would be surprised how many track owners don't understand what a Good vendor can do for their weekly kart count and won't allow you to vend onsite.