Ration Bars are distributed to Gears as a quick, easy source of energy, calories, and nutrients out in the field. They are, apparently, very cheap and easy to produce, which makes them somewhat abundant. Because of this, Ration Bars have been adopted as a sort of ad-hoc currency between the Gears and those less fortunate, such as Stranded.
They seem to be some kind of protein bar, sheathed in a simple but durable foil wrapping. It is unsure what the exact nutritional values are, or how many each Gear has at his/her disposal.