You should carry a spare
bar retainer kit along with a couple of bungee cords for the exact reason you posted about. Also, always make sure you grease the ends of those WD bars where they insert into the hitch head. That slot in the bars needs a bit of grease also so the pins don't wear too fast.
It ia very easy to replace the pin. Just carefully pull out the clip far enough to remove the old pin and put the new one in. You most likely won't need the clips but will have them in case you do.
Barney
Edit:
Here is another.