A backpack or knapsack was a specific type of bag carried on the back. They were key components of backpacking and containing parachutes.
Cold weather gear often included a backpack. (ENT: "The Seventh", "Regeneration", DS9: "The Ascent", VOY: "Timeless") For the recreational activity of orbital skydiving, a backpack was also used to store the parachute. (VOY: "Extreme Risk", Star Trek)
The orbital skydiving backpacks seen in Star Trek were created and provided by the company Quantum Creation FX. [1]
A member of the assault team from Enterprise NX-01 which beamed down to the Vulcan monastery at P'Jem was carrying a backpack. It included phase-pistols, a Vulcan scanner, and a set of micro-charges and a remote control. (ENT: "The Andorian Incident")
The call sheet for this episode is only listing a "small equipment bag" in the props section.
The MACO environmental suits had their support systems located in a backpack. (ENT: "Anomaly (ENT)")
An image of a young Muliq Al Alcazar showed him wearing a backpack. (SNW: "Children of the Comet")
Chief Petty Officer Garison carried a large radio backpack while being part of the landing party which beamed down to Talos IV in 2254. (TOS: "The Cage")
The water mask life support device made use of a backpack. (TAS: "The Time Trap", "The Ambergris Element")
In 2270, an Orion captain was carrying explosives in a backpack he attempts to use for killing James T. Kirk and destroying the USS Enterprise. (TAS: "The Pirates of Orion")
Strike team uniforms were also equipped with backpacks. (Star Trek V: The Final Frontier)
In chapter five of The Doctor's holonovel Photons Be Free, his protagonist had to wear a fifty kilogram backpack version of the mobile emitter. (VOY: "Author, Author")
In 2381, Ensign Beckett Mariner called Knicknac "Knapsack," to which he corrected her, telling her his name was "Knicknac." (LD: "Crisis Point 2: Paradoxus")