Grains and (dried) legumes when combined make a whole protein and a balanced meal. You can survive on this combination very well even if nothing else is around.

The only problem - storage and carriage. It is sensitive to dampness, heat and pests and bulky to carry.

Grains and legumes can be stored for relatively long periods of time.

Grains - better be whole, brown, wild etc, since if all the rest of supply will be cut, then you will want some nutrients (vitamins, minerals, carbohydrates, fats, oils, and protein) in what you have. So if you still buy 'white' grains, maybe it is a good time to switch to more rough forms.

Each grain has its own properties and nutrients, so it might be good to have various types. For example buckwheat is rich in iron. So types of grains that can be bought and stored in advance:
rice
quinoa (btw it is the only one that contains whole protein in itself, without legumes added)
spelt
buckwheat
amaranth
millet
corn or polenta

Beans - these are much faster and easier to cook and consume less water, than other types: lentils(split are even better), split peas and black-eyed peas, these don't need soaking.

Storage of grains a beans:
1. they should be dried, which is usually the case in stores
2. in a dry place (in damp environment, like in a sack on the ground it will take ~3-4 days to the grain to spoil
3. off the ground,
4. storing in sacks is risky (pests and mold), so metal cans/jars is much safer way to store for prolonged periods of time.

Note: refrigerator and underground is a bad idea due to dampness.

Carriage:
In metal cans, not sacks, protected from rain, dampness and sharp temperature changes (as dew can result with too abrupt temperature change, as the water in the air condenses). Spreading water and moist absorbents (SAP) within the can and then placing a sack in it can be considered (so if you didn't throw away all those small packets with SAP coming with various products, time to find out why you didn't throw them away :) ).

For less bulkiness and making the preparation faster and easier, powdering can be the way to do that. Then you can use it as a flour too.

Other uses of grains and beans: any whole dried grain and legume (like rice and beans) can be used as a water-absorbent in salt.

Why you will want to store salt:
Food - minerals source, so it is better to have sea or Himalaya salts (then you'll have various minerals and iodine and not only NaCl)

Usual NaCl salt - as a universal remedy, disinfectant, antifungist :), cleaning substance and body care (like brushing teeth).

Salt can be spread where you want to keep your things safe from fungi or mold spread (like the bottom of toothbrushes glass), or in some damp corners of your house, spread over risky areas, like where the roof or walls become damp, in shoes, socks, or apply salty water directly on feet and air dry (like if you won't have an opportunity to change socks or smth...

So you can use rice for example. It can be placed in small cloth sack and then within the jar. Or if you use the salt cellar (with small holes), then you can just spread rice directly in the salt.

Rice and beans can be also added in this way to garlic powder (which is also good to have on hand during tough times).

... to be continued...

(Just as grains can protect salt, salt can protect grain, from mold, so mixing can be considered if there is a serious mold threat, like relatively high air-humidity)