BP-5 or NRG-5 is a dry biscuit used for disaster relief and emergency rations. "It provides the recommended protein and basic vitamin requirements. Because it is easily digestible, neutral tasting, and contains no dairy or meat products the food may be widely used, even for people with severe malnourishment" according to https://en.wikipedia.org/wiki/BP-5_Compact_Food

Bought in bulk it comes out to about 6-7 EUR/day.

Nutrition facts taken from Autarka and http://survival.4u.org/vorraete/bp5-selbstversuch.htm