The seventh chapter of mishnayos Shabas has this general rule ("כלל"):
Whatever is fit for storing and people store that [amount of it], and he carried it out on Shabas, he's liable therefor to bring a korban chatas. Whatever is not fit for storing, or people don't store that [amount of it], and he carried it out on Shabas, he's not liable, except one who stores it.
The subsequent mishnayos — off and on for the next three chapters (!) — give specific examples of this: how much food is fit for storing, how much wine, how much rope, how much hide, how much ink, how much wood, and so on and so forth.
And this is all codified in the Rambam (Shabas chapter 18), as well as in the halachic restatements of the Rif and Rosh (ad loc.).
But it's not in the Shulchan Aruch. Or at least: There's no reference to Shulchan Aruch in the En Mishpat – Ner Mitzva for any of these mishnayos, and I can't find them in the Shulchan Aruch anywhere.
Why not?
I was thinking to answer as follows (but this answer doesn't work, as I'll show). It may be because Shulchan Aruch is not concerned with nowadays-impractical topics like korbanos. Whether a prohibition is mid'oraysa (divinely imposed) or mid'rabanan (rabbinically imposed) is important even nowadays, but — I thought — carrying out even less than a worthwhile amount of a substance is forbidden mid'oraysa (because of the principle of "chatzi shiur asur min hatora", "a part-measure is forbidden mid'oraysa"), which renders these mishnayos relevant only to the issue of korban and thus moot nowadays. However, that's not the case: Aruch Hashulchan (301:34) clarifies that "a part-measure for all labors except carrying out is forbidden mid'oraysa". So that proposed answer doesn't work.
