German Bundeswehr issued OD (military surplus) compression bags. The outside are all in pretty good shape but the waterproofing on the insides have started to fall apart. 

Compression bags are mean for sleep systems (sleeping bags, ponchos, poncho liners, wool blankets etc) with outter straps for you to be able to “compress” your sleeping equipment down to make it take up less space inside of your backpack. 

Sizing:

Small:  16" x 11"~ 5.5oz

Large:  22" x 14", ~7.1oz