You can't "save seats" as we said as kids...
If you leave then you are no longer camping, and the spot is open. It is free camping, no registration, no reservation and no holding, otherwise people would block off all the spots forever.
If you have a tent left behind then that is considered active camping and people will generally not take your spot unless tent is abandon overnight.
If you leave a chair, good luck with that, as you not only are giving up your camp spot but maybe the chair too.
Again, generally people are considerate and there are plenty of camp spots so a note or some stuff left behind that does not look like it was forgotten or abandon will suffice.
The hard rule is that the camp spot is only yours as long as you are there, when you leave it becomes open and if you leave junk behind then you are a litter bug.
What you will want to do is break down camp, go touring around then find another spot the next night. Don't try to hold spots while you are not there, as someone else might want to enjoy that spot during the day instead of you left-behind trash, also, since it is not a real campground there is another rule: finders keepers, which goes for your abandon stuff too. Rarely there might be someone who will argue that it is not your chair. You will be buying a new chair if that ever happens.