You can also find plenty of campsites without reservations when camping in places and at times that other campers don't care for.
We once went RV-ing across the U.S. back to the East Coast from CA, using the Southern Route in July and August. Hotter than blazes and wetter than the Congo - but we had campgrounds and campsites to ourselves with no reservations. We also had good air conditioning and generator systems!!
Free as a bird campsite-wise on a multi-thousand mile trip ... but we'll NEVER DO IT AGAIN on that route at that time of the year.
