500 cc oxygen absorbers. They are small iron powder packets used to absorb oxygen in packets, cans or buckets for extended shelf life.
Oxygen absorbers are small packets of iron powder that allow oxygen and moisture to enter the absorber but does not allow the powder to leak out. Absorbers increase the storage life of food and they are safe to place in containers with the food. One 500 cc absorber is recommended for mylar bags or #10 cans.