Any item fit for storage, which [people value enough to] store—if one carried it out on Shabbat—that person [is held liable for a Shabbat violation and] must bring a sin offering. But any item not fit for storage, which [people do not generally value enough to] store—if one carried it out on Shabbat—only that person who [valued it enough] to store it [is held liable for a Shabbat violation and] must [bring a sin offering].
One who carries wine out [from domain to domain on Shabbat, only violates the prohibition] if there is enough to pour a cup. Milk—if there is enough for one gulp. Honey—if there is enough to spread on a [minor] wound. Oil—if there is enough to anoint a small limb. Water—if there is enough to moisten a compress. All other liquids, if there is a quarter [of a log, roughly four and a half ounces] . . .
I mentioned last week, in passing, that one violates the prohibition of carrying from domain to domain on Shabbat if one carries an object of value. How do we measure the value of objects? The Mishnah makes this measurement by noting the things that people save. Mishnah Shabbat 7:3 presents the abstract principle that anything which can be stored for some period of time (in the days before artificial refrigeration) and which people do, in fact, care enough about to store, is deemed to have value. In Mishnah Shabbat 8:1, we see a concrete example—liquids like wine, milk, honey, oil, and water are valuable and we make an effort to store them in conditions that will preserve them for as long as possible. However, at a certain point we consume enough of a liquid that the remains are too small for us to bother saving. It is simply too much trouble for most people to maintain less than a cup of wine or a gulp of milk.
However, the second half of Mishnah Shabbat 7:3 recognizes that there are people who value these small amounts, or seemingly trivial objects. Though for most people, carrying less than a mouthful of milk out of the house might not result in a Torah-level violation of Shabbat, for a person who would hold on to that "trivial" amount of milk, it would. So, oddly, two Jews can perform the same act of carrying, but only one may have violated Shabbat on a Torah level. This oddness may have been one of the reasons that our sages tell us to empty our pockets completely prior to Shabbat, carrying no burdens of any sort. Shabbat is a time when we put things of material value a bit to the side, so that other sorts of value can have precedence.