From Halopedia, the Halo wiki
Most UNSC combatant personnel carry rucksacks in the field to store small items and matériel for their personal use. The UNSC Armed Forces employ various types of rucksack, from more traditional fabric backpacks to the hardened cases employed by ODSTs and composite backpacks used by the Spartan-IIIs in conjunction with their SPI armor.
A routine packing of a UNSC rucksack typically contains a set of items arranged in specific layers and includes spare clothing (namely shirts, socks and underwear), extra ammunition, a mess kit, first-aid supplies, solid fuel pellets, signaling equipment, snares and fishing line, and personal hygiene products. Various personal effects may also be included. A standard UNSC infantry rucksack weighs 25 kilograms when fully packed for a march.
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