Universal backpack of the Soviet soldier. Suitable for reenactment, model of the WW2. Produced in the mid-XX century for the army.
The word "sidor" call things that men collect when go to jail: a basic kit. At the heart of the design is a very old and reliable principle of tightening the neck straps. Such bags were used in the Crimean war and is used to present days (only the details change). Before the war it was officially replaced with the rucksack (mod. 1939), but remains popular due to simple and robust design.
It is impossible to lose something from the Sidor, because it is either tightened off or you can't wear it.