A Sydney police officer left his gun and 30 rounds of ammunition in a backpack at a McDonald's restaurant, which was then stolen and has never been recovered.

The incident in Mascot is among dozens of examples of NSW police officers losing guns, expandable batons, handcuffs, portable radios and breath-test devices in the past three years.

From a police baton being lost while an officer moved house, to a set of handcuffs vanishing when an officer retired, the list of unrecovered items, obtained under Freedom of Information laws, reveals a large loot of police gear now potentially floating around the underworld.

Just one gun has gone missing since 2013, but 29 batons, 24 sets of handcuffs, 27 hand-held breath-test devices and 16 portable radios have not been recovered in the same period.