It is smart to build up spots well ahead of time so that you have more time for nature to partially take things back over before you really put it to use. Letting things like disturbed dirt and vegetation settle out and regrow.
I had set up a small string of emergency flood drainage ditches on a property in CA years ago, then got bored, had the tools around, and turned it into a trenchwork with a couple of fighting positions that had overhead cover from pallets covered again with some plastic and dirt over the top, then I tossed grass seed around to obscure the amount of work that had actually been done. Grass crew up in the "bunkers" to the point they would have been impossible to tell from right on top of them, and putting them back to use was just a matter of stomping the grass down.
I think some later tenants on the property just used them for an illegal garbage dump and covered them up.
What I see would effectively be construction of discreet campground facilities with latrines, improved parking and drainage. Trees and large bushes groomed to act as cover and camo net tie-in points. Lay in low value bulk supplies that people are unlikely to want to bug out with but can enhance quality of life at the place if it becomes occupied full time.
Wells, cisterns, even a buried fuel tank that you would keep empty if you are really cheapskate about it, but have out there available to fill up as a fuel depot if you were to need it.
Latrine and garbage pit construction - digging, some construction, building the toilets, putting toilet paper in storage at the latrine points.
Water collection and distribution points (important in western states) - running water lines from a water source to a collection point (may or may not remain hooked up). Running water lines from the main collection point to a few distribution points. Pot growers in Northern California are masters of that sort of thing. They use a lot of the kind of black hose tubing that landscapers use to lay in sprinkler systems. Systems involve things like plastic barrels, sometimes larger water tanks. Some cheap sneaky ones involve those little children's backyard wading pools just set in the ground and covered with black tarp material (black is used a lot to reduce freeze damage). Greywater drainage is done with drainage tile, and that is sometimes used for sewage running to dirt bunker type septic tanks (they never get emptied, just covered over when full). The greywater and septic tank system is an issue if you are setting it up as an RV compatible site.
Fuel storage is usually best dealt with by pre-staging drums and pumps for the drums. Pre-staging fuel stores is a hotly debated issue, especially when some people start hogging fuel that others bought. At least the drums are not terribly expensive and can be used for a lot of stuff if you have even rudimentary welding and fabrication skills and equipment. Super cheapskate scenario is you pre-stage drums, then when you get out there in a bugout, you are likely going to be on some sorts of gas rationing systems anyway. You pull your vehicles up to the fuel point and siphon some fuel into the buried drums then go back out to civilization and buy or otherwise obtain your rations of gas, all while building up what would probably be an illegal but highly prized stash of fuel.
Power, well there is the off the grid stuff. Solar is not something I would leave out on site due to country scavengers, unless I had gotten the panels cheap, or by scavenging, or had pretty good security control on the property 24/7/365 anyway, like when you are prepping a rural property for larger scale use. You can plot out the panel points, maybe pre-lay some wire scavenged from abandoned or condemned buildings.
You can pre-lay wire for your on site hardwire commo, like field phones or a simple phone or internet system. Pre-laid network cable would allow for silent and fairly secure commo at the site.
There are some food crops that you can pre-plant which will either A: be edible at least part of the year you are out there or B: attract game animals that feed around your semi-abandoned crop sites. This can include fruit trees, berry bushes, corn, soybeans, horse feed type stuff, maybe beans. I understand that tomato plants are a gamble unless they are cultivated and heavily fertilized the first year and get large enough to survive the freeze cycles through winter, but if you can get a large strand of tomatoes to grow feral then that's a pretty good food source.
If you prune trees right, you can hide entire roads from the air, especially the meandering track type roads. I did some work in Manzanita bushes in Northern CA where basically "hollowing" them out over the course of a few years made it where you could pull a truck under them and have a nice shaded spot, good cover from the air and ground level observation, and actual security because of controlled access points combined with other parts left feral meant you could not be approached from just any direction. Criminals turned that whole place into an operation when I moved away, and I heard did everything from running a chop shop in there to cooking meth.
Something I did on an Oregon property was cultivate the blackberries around old scrap fencing, to the point that the hedge barriers could stop a tank. Maybe not stop him cold, but damn sure jam up the tracks badly, more so than concertina wire. For that matter, a site can be set up with old surplus concertina wire (obtained for next to nothing around military bases, and sometimes they might even pay you to take it away) and then your concertina wire barriers planted with blackberry bushes and other greenage. Blackberries and concertina - that's what you call some barrier security and one good growing season into it, an irregular shape barrier network will be impossible to tell from the air.