Radius Engineering makes their own "bunkers" sized with a capacity ranging from 5 people to 2000.
Their bunkers are plastic shells that are buried underground. Some of their designs have open spaces large enough to allow for the construction of "buildings" (more like tiny 3 story apartment blocks) for people to live in.
The outer and inner walls of these structures can not rust. They also have environmental systems that will maintain temperature and air quality for 5 years (food stores for that long as well).
If someone was to lower the number of "residents" and stock in lots of freeze dried food, they might have food for 25 years (if there is enough space for the food). The plan would have to call for eventual underground food production.
The main problem at that point would be power. Rather than use nuclear power, geothermal electric generating turbines might be more viable. Efficiency is not much of an issue when need is the most important factor. Electricity must be provided (or slaves to turn lots of hand cranks) Ember used an underground river. This might also be a viable power source.
If all the lighting was LED power draw would be low.
Growing new food would take up lots of power, but using the new Sulfur bulbs that produce near full spectrum light using about the same amount of power as LEDs (as opposed to Metal Halide grow light bulbs), the residents may be able to grow their own food.
Plant crops, berries, and even Mangos would be useful (mangos grow quick and produce wood useful for building. The trees are usually chopped down and replaced quickly because they only fruit for a few years.
Lots of herbs and spices would be good for flavor as well as adding vitamins and nutrients.
Fish and chickens or small goats would be good for meat.
Vat grown protein like Quorn brand would be immensely helpful for varying diets.
Appliances would have to be kept to a minimum. TVs would probably have to be concentrated in the Pub(s) or common areas. Likewise, fans, hair dryers and other electrical draws would have to be carefully planned for to avoid brownouts.
A single movie "theater" with a huge DVD collection and projector would be more efficient than everyone having their own home movie night.
If human, plant and animal waste is recycled either to grow crops or in a methane digester, they would also have access to a gas that could substitute for LP or natural gas and would allow cooking without using electricity.
The Geothermal piping might also be useful for creating radiant heat cook ovens as well as a way to heat the building and run refrigerators without using electrical power (Methane could also be used to power LP camper refrigerators.
Spare parts for all of these things would be something that you could stock, but at some point they would start running out so a machine shop with a large supply of tools and bits as well as metal stock of all kinds would be very important to keep things running.
Just a few thoughts on the subject
WPD