We usually can always find a local selling wood very close to the campground, if we feel it necessary. We usually by some from the CG and some from the local to balance things.
I will say one thing we started doing our "long trip" is to go hunting for leftover wood every other day or so. People will pull out and sometimes leave any leftover wood sitting there. We started taking a pull behind trailer for our bikes (the ones kids ride in) and haul it back to our site that way. We find that way we usually only have to buy wood once or twice during our entire stay.