Hi! There's lots of room for more info on salt in particular, or S&P as a pairing, but fyi, you can get started on pepper with a post in the FAQ section Food seasonings:
Salt has always been around: a small amount of sodium (perhaps 0.2g daily, 0.5g of salt) is necessary for our bodily functioning, though much of it can be found naturally occurring in foodstuffs, and it's been used for probably millennia to preserve meat & fish, so that even at the start of the modern period tens of thousand of tons of the stuff were being traded around the Baltic and western Europe.
Pepper was known in the ancient Mediterranean but long a luxury, despite being imported from the 12th century through Venice and Genoa. European consumption may have risen by the 15th century to 1,000 tons, only 15g per head annually: with the discovery of the Cape route to the east in 1497 this rose by the early 17th century to 3,000 tons or more (30g per head). But prices remained high and were maintained by limiting shipments, and by the late 18th century imports probably came to less than £350,000. The spice seems to have become truly a mass consumer good only with the passing of monopoly trading companies, the tripling of western incomes and more than twentyfold growth of world trade in the century to 1914, though data are fiendishly hard to come by.