Recently I visited one of the NFS campgrounds on the coast of California. I did not have a reservation but lucked-out and secured a spot. I immediately paid for the duration of my planned stay and as required posted my payment "stub" on the numbered marker post at the site. A couple of days later we decided to take a drive up the coast for the day and then return later to our pre-paid camp spot. Being in an RV and not having a tow vehicle, we left our spot for the day assuming it was reserved for us by the "stub" on the post (we did not leave any gear at the spot). When we returned the camp host had pulled our "stub" and given the spot to another party. The host was adamant that even a paid-up spot is surrendered if something isn't left behind at the site. My question is - What is the proper etiquette for insuring that a site is retained when one leaves a campground for the day? Do I really have to leave some unsecured gear behind?

I don't know what the "rules" are, but if we were in your position, we would have stopped by the Host's site to let them know that we were going to be gone for the day but that we'd be back. That certainly *should* have prevented them from giving your site to someone else...otherwise, how is the Host supposed to know that you will be returning instead of deciding you didn't want to stay longer (even though you'd paid for more days)? If I'd been the Host, without any information to the contrary, I would have assumed that you'd just decided to leave and weren't returning.

So, either notify the Host before you leave or leave something in your spot. I've always thought that a cheap tent set up in a spot would be a good thing to leave behind.

Most people leave a lawn chair or some other item in the space to indicate that it is occupied. I have seen red cones or signs used that say "occupied". Sorry about your mis-adventure.

My husband and I do camp hosting in the National Forest. When we volunteered in Indiana a lot of folks would put there stub on the post and not take it down when their time was up. So most of the campers didn't pay attention to that. The park had some occupied signs they would give out for use but most folks just left a chair or something.
Where we're at now there just my husband and myself. We try to know what is going on with the sites. We've personal made a few occupied signs that the campers can use. It's not unusually for folks to leave early ..some tells some don't. Most of those that don't say anything are the ones that leave and won't finish the time they paid for. We have a small number of water/electric sites and sometimes have had to turn folks way. So if we don't know you'll be back or you haven't left something on the site and there is no other site for the camper coming in we will rent that site out.
If the gate house is manned by different folks besides letting them know I would leave something on site as some times information gets lost between shifts

To prevent any conflicks when I host I consider a paid site occupied untill the expiration of the payment date unless the camper tells me that they are leaving.

You have probably figured out by now that the wise thing is to leave something around and any of the items mentioned will do. But I think it's unfortunate that your experience turned out the way it did. I can understand that another camper moving in might miss the tag on the post
(and if he's like me he might not even know the date anyway!). But I feel that that's one of the things the host is there for and for the host to assume that you have left permanently because you are not there is plain wrong. Frankly I'm surprised to see that some agree with his actions. Voodoo has it right; lacking any knowledge to the contrary, it should be assumed that you will occupy the site as long as you have paid for it.
Another consideration is the rule , stated in many campgrounds, but enforced in few, that a campsite must be physically occupied on the first night it is paid for. I know that was not the case with you, so we best leave that discussion for another day. Hope the rest of your trip was better.
Ed

I would say make sure you confer with the host. If they know you haven't left permanently you can usually come right back.

All good advice. However, one scenario was omitted - when there is no CG host. This can be because it is off season or the CG simply has no host. Everyone should know the latter, in particular, is significant. My thought is if there is no host and the rig will be removed temporarily from the site, consider another campground with a host and follow the advise above. Calling the ranger district office ahead of time to determine the CG host status might be a good idea too.

Lastly, in regard to leaving an item behind at the site, consider purchasing one of those little plastic easel-like stands - about a foot or so high and affix an "occupied" sign to it. If it gets stolen no big loss except to make one angry . . . Fred

My solution is to leave the "standard" red and white checkered tablecloth on the table. It is very visible, is not a likely target for theft, and is cheap enough that a loss would not be a big deal.