When a paddle finishes at a different place from where it starts, it is necessary to figure out a way of getting back to the launch site to collect any cars left there. This is typically handled using a car shuttle, or car shuffle as it is known by some people.
The trick is to begin the day with all paddle craft at the starting point and enough cars (or more specifically seats) at the finishing point to return drivers to cars left at the start. Unless the paddling equipment belonging to those drivers can also be returned to the start, they then need to drive back to the finishing point to collect it.
One or more people are usually appointed to mind the paddling equipment while this happens. If that is not possible, it will need to be secured in some other way. Lockable tie-downs and twisted wire cables with keyed or combination locks are useful for this purpose.