Block states from imposing residency requirements and taxes against Military members and their dependents. Key examples include driver's licensing and vehicle registration do to a member being stationed outside of their home state. It should also block states from taxing them under certain conditions: if home state charges income taxes then service members are exempt from sales tax and vice versa (no taxation without representation). Taxes on products purchased out of state should also be blocked for everyone.
Example scenario: a resident from Montana is stationed overseas and purchases a car, they are then ordered to a duty station in Kentucky. Kentucky would then impose sales tax on top of vehicle fees and other taxes where as the home state would not impose the sales tax.