No reservations here. Not even for Grand Teton National Park over the July 4th holiday last month.
The trick is to get where you are going by mid afternoon. Get someplace for the weekend on Friday & sit tight till Sunday. Oh yeah, be flexible. If plan A falls through, have a plan B. If that fails too there is always something, even if it is Walmart.
We have rolled into the Grand Canyon south rim with no reservations too. Also Yellowstone Bridge Bay CG, no reservation.
The FHU & pull through sites go first, then the W/E. If you can survive a few days dry camping & know how to reverse, getting a no reservation site becomes much easier.