A single serving is a food product sold in portions intended to be eaten completely after opening the packaging. Notable food items of this variety include candy bars, small chip bags, pudding cups, and soda cans. These contrast with multi-serving products which list servings per container and ingredients which aren't intended to be eaten without preparation. While single serving products are most often encountered in checkout lines and vending machines they also show up in box meals and even some restaurant combos such as potato chips in sub shops. Single servings have a lower class connotation because the super majority of them are cheap, lower nutrition, high calorie, mass produced products which leave the maximum amount of packaging waste per unit of food. The price also tends to be higher per ounce.
Single serving can also be used metaphorically to describe something of brief scope and singular instance. This is most memorably described in Fight Club's single-serving friend. Most things can in principle be boiled down to a one time use smallest salable unit: individual condoms, two aspirin tablets in a wrapper, a single tab of blotter paper, or one stick of dynamite. Since the word serving is typically reserved for food and drink it's not fully applicable but the concept comes through. Single serving items are a potent symbol of the modern world. They reflect both the prodigious fecundity of industrial output and the disposable transience it encourages. One's feelings about this are likely to wax and wane with how badly they need an ibuprofen and a bag of peanut M&Ms from the gas station. Convenience's war on our bank accounts and the environment rages eternal.
IRON NODER XVIII: NEGLIGENCE IS THE RUST OF THE SOUL