We camped in the summer when the kids were young. We normally made reservations. We occasionally camp in the summer with the grand kids and have always made reservations. Usually,you can normally find an open spot for one night when you're traveling unless it's a holiday weekend. For longer stays I would make reservations. And it's easier to get them if you book from Sunday through Thursday. The weekends are much harder to get a site the longer you wait to book. If you can still camp in the off season, that's best. Easier to get sites and less people. We went to Yellowstone in May. We had a reservation for the first night because it was a Saturday. We also had reservations in Yellowstone for Wednesday through Saturday. But the rest of the trip we didn't have reservations. We stayed mostly at state parks and paid anywhere from $16 to $26 for sites with electric.I tried to figure how far we would go in one day and then find a state park close by. It worked out very well.