why wheat

Food stores are useful to have for a variety of shocks and emergencies.  Rice exhibits survival over a large temperature range.  Oats are edible raw.  Soy contains all essential Amino Acids.  Other crops probably grow on marginal land.  But it is wheat that is most storable under appropriate conditions:  cool, dry, protected from insects, vermin, fungi, etc.  Edible wheat has been recovered from the pyramids thousands of years old.  Wheat presently costs 2% of crop cost, to store in modern silos.  Mostly this is the cost of drying and refrigeration.
There are potential ways of decreasing this cost:  Novel polymer bags, new silos and storage bins, GMO varieties, the presence of permafrost suggests refrigeration costs can be lowered.  Other food crops might be engineered one day to bequeath the storability of wheat.  Most of the oil in wheat is in the wheat germ, which is not stored in silos.
Spelt wheat.  An uncommon variety, by virtue of its hard covering Spelt is particularly resilient.