Missing originals
Exceedingly random thought!!
For most plant-based food items, regular grocery stores sell both the raw or dried original item and hundreds of processed and prepared products derived from the original. Juice, powder, smoothies, jelly, soup, sauce, salad, stew, fried breads, baked breads, cakes ....
I can only think of two exceptions to this rule. These two are probably the MOST common items in a typical diet, so the exceptionality is itself exceptional.
Sugar and wheat.
Unless I've missed it, you can't buy chopped or dried sugar cane, and you can't buy bags of wheat kernels in the usual Safeway or Yoke's or Albertsons. You can definitely get wheat in 'health food' stores but I doubt you can get sugar cane anywhere.
Missing sugar makes sense. You can't do much with raw sugar cane, and processing it into powder is complex and industrial. 100 years ago sugar cane was a common crop in Texas and Louisiana, and sugar cane was
sometimes used directly as a sweetener in homemade jellies or pickles, but I don't find any record of home processing.
Missing wheat doesn't make a lick of sense. Lots of people bake bread, and some of them prefer to grind their own flour. It used to be universal and it's still fairly common.
I checked this morning when I was buying my usual pound of barley. In the same aisle with barley, Safeway has several kinds of rice, several beans, lentils, and Keen-Wah or Ah-Ooh-Gah or whatever it's called. No, I guess Ah-Ooh-Gah is some kind of greens.
But no wheat at all.