Oh yes book a National Park membership. It will give you cheaper access to them and you can then use their campgrounds too. If you are visiting more than 3 National Park I think I remember it worth it. Same for State Parks, but they don't cross over to another state, so it depends on where you are planning to camp/ride in that state. Also remember they have these options in the park - hike and ride (I think I remember they are called) you get cheaper camping, often a little further away from the other campers and facilities, but you got access to it all.