@Laura2592 , I leave enough, plus a bit, for their stay and tell them if they find they need more, just to ask. If they ask, I leave a bagful for them beside their car, which they then have to fetch and carry a kilometre back to the treehouse. If they use that up, they have to ask again. By that point they are using too much in anyone's books, and cannot complain.
In the old days, when I stacked extra at the treehouse to save myself work at turnovers, some would burn through shocking amounts. When they have to lug in the extra themselves, they are more frugal.
Also, it all works out in the end. Some guests burn everything just for the sake of it, and others don't bother or have no fire-lighting skills, as shown in the sad crumpled and charred newspaper they leave behind.
So no, there is no set amount, but I've put a damper on burning whatever they want by making them work for it.