I always have a few trips in the planning stage. When I hear about a destination or a trail that I'd like to do someday, it gets a file on the computer. Related information gets added over time -- nearby places, restaurants that sound unique, maybe some oddball lodging, little known spots gleaned from forums like this or elsewhere on the net, etc. Eventually I'll begin mapping a potential trip on Garmin Base Camp with information pulled off maps, Google Earth, shared .gpx files, etc. Some climatology data will tell me the best time of year for the potential adventure. With all that, I can begin to work my vacation schedule and then the serious planning comes together.
As some have said, there are places that require reservations. Those become "hard points" in the plan. There may be some places that I just have to see on this trip. Those too are "hard points", though not fixed in the timeline usually.
Here in the Southwest we are blessed with a lot of open land, so boondocking a campsite can be easy, well until the sun is setting and there doesn't seem to be much around. So along potential routes I'll use Google Earth and get coordinates on what might be usable sites. There are some sites like freecampsites.net that are a good resource as well. Having a some backups makes looking for that perfect spot a little less stressful. The potential campsites go into the appropriate Garmin Base Camp folder with whatever information is available. Routing, alternate routes in case something blocks our path, fuel availability, places to replenish supplies, potential hikes, etc get filled in as soft spots.
From there an itinerary begins to form. Reservations for the "hard" points made with ample time between them to do what else I have planned plus some extra time for the unforeseen, good and bad. Distances computed with both time and fuel in mind. Meals planned out. Getting closer to departure information on weather forecasts and road conditions /closures are added. The Garmin Base Camp data is transferred to both my Garmin Oregon and my HEMA maps app on the iPad. Some destinations are also put in the onboard nav system in the 4Runner. Benchmark state maps are always onboard as a back up. We have a pretty standard load out, but any particular needs for that trip are added in. With the weather data in hand clothes are chosen. For extended or complex trips I build a book with most of the planning data for quick reference.
Finally the plan is passed along to trusted friends and family. Always a good idea for someone to know where you place to go. Since our trips are usually single vehicle, we use an InReach for more remote trips so the folks back home can check on our progress and the ability to call for help should it be needed.
There is obviously more that goes into it than this, but you get the idea. I find out if the trip is well planned there is actually more ability to take advantage of unexpected opportunities while insuring some level of comfort, safety and enjoyment.
