This upgrade allows gear to carry smaller gear within or on it, in an obvious compartment. Equipment with the storage capacity upgrade can hold multiple items at least one size smaller than the equipment itself, as long as their total weight is less than the equipment with storage capacity. Thus, a blaster rifle (Medium weapons, Tiny object, 4.5 kg) with storage capacity might hold eight frag grenades (Fine object, 0.5 kg) and five power packs (fine object, 0.1 kg) securely in external straps and pouches.

Source: Scum and Villainy, p. 42