I want to put a car in storage, with the idea that it will be ready to use at a moment's notice. What are some considerations?

How Long is storage. A few days a few months or YEARS. Indoor? Outdoor? Temperature controlled. (Heated in Winter Not extremely Hot in summer)

Some reason in particular you cannot go to your car and check it every few months. Start it up let it run to charge the battery circulate the fluids.
Have the car completely serviced before Parking. Fresh Oil Fresh Battery
GASOLINE does not store for a very long time.
. You should also purchase a fuel stabilizer such as Sta-bil, to prevent ethanol buildup and protect the engine from gum, varnish and rust. The fuel stabilizer will prevent the gas from deteriorating for up to 12 months.
Be prepared to bring a Jerry Can of Fresh Gas to get it started and away from the storage place.

YES dry rot happens It takes YEARS No reason you cannot have a few back up items you can easily change yourself.
Lubricate the car. Oil the hinges of the hood, doors, and trunk. Use a graphite-based lubricant for locks. Coat rubber parts of the doors and tires with silicone or white lithium grease. This will help prevent them from freezing shut.
Remove wiper blades or lift them up so they do not become deformed or flat.
CLEAN the car Inside and out.
The car will not store forever and start immediately. It is easy to Bring a New Battery for example when you need the Fast Exit. Have a Jump start thing Available if necessary.
Can keep some Oil and other fluids in the trunk for down the road. CHANGE them Annually.
Keep a simple Tool Box in the car. Have tools for repairs YOU KNOW HOW TO DO.

TIRES can Flatten over time. Might want to have An air pump available.Spare tires Mounted on wheels. Can be stored inside the car. If not needed just leave behind when you go.

May want to consider Jacking the car up placing on stands and removing tires. They Do get flat spots.
Have some Paper Maps. Detailed for the nearby places. Then for the adjacent states. You might not have your electronic gadget the First Bit of your Escape.

Maintain Insurance on it. Keep the Tags CURRENT

Get Back in Action
Here's a checklist of what to do when you're ready to bring your vehicle out of storage:

Check under the hood for any evidence of rodents. Look for chewed belts, hoses, wires or nests. If you covered the muffler or air intake, remove that material before you start the car.
Check the windshield wipers to see if the rubber is cracked or brittle.
Check tire pressure and inflate the tires to the recommended specs.
Check the brakes. Rust may have accumulated on the rotors. In most cases, this should go away after you drive the vehicle for a short time.
Check fluids to make sure there have been no leaks and that they are at the recommended levels.
If the battery cable has been disconnected, make sure that you reconnect it and that the battery terminals are clean.
Wash your vehicle to remove any dirt that may have accumulated.

You can store a few days worth of emergency food (CHANGE IT every few months) Basic Emergency Survival Kit. A change of clothes or two, A Blanket and so on.
Might want to hide some cash. DO NOT just stuff it all in one place. HINT might need to get some gas for your exit.

Many survivalist sites you can check for more details. May want to open a couple of bank accounts at other Banks out of state. You could leave the cards in the car.

Keep It Covered Keeps the dust out.
Cheap Trickle Charger to keep the Battery Charged. (Could be a Solar Powered one)

CHOCK the wheels to stop from Moving. DO NOT use the Parking Brake.It might not release easily.
YOU need to take appropriate things if the storage place has either very cold or very Hot temperatures.
For very cold you would empty the windshield washer fluid for example.

COST of all this????? Maybe just stash some money in some other Banks (Out of State) Get a Bus ticket go Fetch get a car there and then go.

You would be better off putting enough money away and just buying a car when you need it. You will KNOW it is good to go and you won't have to worry about it.

It you do ANYTHING to prep the car for storage, is WON'T be ready for use at a moments notice. If you leave it unused for more than month or 2 without either driving it, or prepping it for long term storage, it will deteriorate.

In short, you plan CAN'T work.

Change coolant, and oil. Drain ALL of the fuel. Belts and tires should last a good 20 years. I am still running one set of tires that was purchased new in 1961. You need to keep vermin out of it. Mice or rats can do the job on wiring in no time. You will need to stop and get a battery for it on the way to retrieve it.