A backpack was an object carried upon the back used to carry items. Using minimal technology, the backpack was widely used throughout the galaxy. Luke Skywalker had a blue colored backpack made on Dantooine out of gundark-skin. It possessed many pockets, which Skywalker used while on patrol to hold supplies. Skywalker wore it on Dagobah, when he was under Yoda's tutelage. Yoda rode inside the backpack at least once, instructing Luke during a training run.
Clone troopers and some Jedi carried backpacks during battles in the Clone Wars. Republic commandos carried grenades and other items in backpacks. Clone trooper medics carried backpacks of medical equipment.
Later, Imperial stormtroopers carried backpacks during certain operations that required them to be independent and self-sufficient for long periods of time. The standard private stormtrooper backpack was equipped with an orange pauldron and contained E-11 energy cells among many other items.