While sometimes having too much time on my hands, I've put some thought into this. This will probably go into more than just what to bring.
First, remember, construction underground requires some careful consideration. You wouldn't want some archeologist 500 years from now discovering
your crushed body with all your unopened canned food because your shelter collapsed on you. Consult an engineer familiar with this type of
Second, it would depend on your shelter.
- Is it a large shelter intended for a long stay or just a small room to survive a few days in? Of course this will be the first thing you must answer
before you decide what to stock it with. A small room for only a few days will only require the bare necessities.
You will need a means of circulating air through your shelter. If you plan on surviving biological/chemical threats you will also have to install some
sort of filtration. This creates some complication because now you will need to provide electricity either from the power grid or battery power.
Preferably both. You can use the main power and keep the batteries ready if the main power fails. There are systems available which will draw from the
main power and automatically switch to battery if it fails. You will then need a means of recharging your batteries or use a manual pump. I would plan
on some sort of solar or wind power to at least recharge the batteries. Now the problem of having these exposed arises. Solar/wind power generators
could be destroyed in a disaster or simply stolen while you are underground.
Water. For a few days you can probably get away with 5-10 gallons. Figure about a gallon per day per person.
Food. A short term supply could really be anything that you can store a short while without spoiling. It's not going to be very much so you can
easily rotate it. Canned goods would probably be all you need. You can get just about anything in a can. Don't forget the can opener.
Some sort of port-a-potty type thing.
A radio, some lights and plenty of batteries. I suppose you could run a metal rod or coax to the surface to receive radio signals.
Some books or other entertainment.
For a large shelter intended for extended periods you really need to plan things out. Especially if your plan is lock yourself in and not leave at all
for any reason.
Will you be able to store a years supply of food and water?
Will you be able to get rid of a years supply of garbage, waste?
What will you do in case of sickness or injury? You can still hurt yourself locked in your shelter.
How will you know what's going on outside?
What will you do to keep from going crazy living underground without any contact?
Some sort of permanent electrical supply will be needed to power air pumps, radios, lights, 2-way radios if you want them, electric stove, etc...
If it were me and I had a large amount of funds to invest in it, I would plan to make it much like I would a regular home as far as living space.
A solar/wind power supply would be essential. The problem is how to defend it. I haven't really come up with a simple way.
I would have a septic tank installed. Don't want to store bags of crap(literally).
Install one of these:
Kitchen, living room, bedroom, bathroom, storage room(s).
If I were planning a new construction I would have a well drilled that is accessible from inside the shelter. Hook up an electric pump but also have a
means of pumping manually. The pump could supply water to a kitchen and bathroom.
I would also have a separate water storage tank installed/constructed as a backup. 500-1000 gallons.
All inlets/outlets would have a valve to shut them off. Drains, water pipes, toilet, air intake/outlet...
Now, what to bring? Whatever you think you'll need for a year.