Standardized, prepackaged rations were a novelty at best for most armies during World War II. Only the United States and Britain really produced and issued them in large numbers, and even then in a supplementary role - the c-rations and k-rations were meant to last a unit until it could receive cooked food from a field kitchen. The Germans made some efforts in this direction, especially late in the war, and they did produce "iron rations" - that is, canned emergency rations that could only be eaten with your officer's permission - but it was a drop in the bucket.

The vast majority of German and Soviet soldiers received their meals from field kitchens. These kitchens were attached to companies or battalions and prepared food in bulk. Runners from the combat units then brought the food back to their units. This system was, obviously, prone to breaking down under adverse conditions. Advancing troops could become separated from their cooks, or the field kitchen could be wiped out, or any number of things could contrive to part soldiers from their food. During the Ardennes offensive, some German soldiers went days without eating after outrunning their field kitchens.

As far as what they ate? In the German Army, the field diet consisted largely of bread, soup (especially pea), margarine or butter, chocolate, coffee, and the like. Bread was also the staple of the Soviet military diet.