This is The First Half of Five Rations Packing Cardboard Box.
5 Menus to choose from.
The 10 in 1 Ration Pack contained two of these cardboard boxes along with two of the 2nd half fiber boxes.
The boxes are machine cut, printed and have the proper fabric tape in the corner to hold them together.
These boxes are the same size as the WW2 equivalents , they are not off the shelf standard sized boxes.