These are British military issue rucksack (pack) covers in Desert DPM camouflage. This two-tone camouflage pattern was designed by the British military for use in arid environments. These are made of a 70/30 cotton/polyester blend and feature an elastic band that secures the cover around the pack. The small size fits up to about a 40 Liter pack, and large will fit rucksacks up to 110 Liters in volume.
These pack covers have been previously used by the British military and are in very good condition, showing only very minor signs of use.
Cool thing over the U.S. covers is the drawstring.