German period rectangular aluminum food tin. Essentially a sort of lunch box which enjoyed many decades of popularity, starting around the 1920's. There is a foldable handle on the top and bottom. The inside has ribs on both sides (possibly to reinforce the side?). It is in OK condition with some dirt, general wear and light dings. Needs cleaned. A good candidate to take out in the field.
This style tin, with the side reinforcements, is pictured on the cover of Der Sportler from 1939.