The main risk is not slowness, but crowding the entrance with both people and items
After a break, everyone often comes back carrying drinks, snacks, bags and jackets.
If all of that reaches the door together, order usually collapses before the car even moves.
Seat the people who need stability first, then deal with objects
Helping seniors and children sit first stabilizes the most important positions in the cabin.
Once that is done, the rest of the car usually becomes much easier to sort.
Trying to hand out things while boarding often destroys the gain of a short stop
Passing drinks or snacks seat by seat during boarding may feel efficient.
In practice, it often leaves several people paused in the aisle doing second tasks.
Before departure, check three things and the restart usually stays clean
Make sure everyone is seated, the door and aisle are clear, and high-frequency items are back in their assigned zones.
Those three checks usually prevent short-stop disorder from spreading into the next road segment.