Grape Nuts - Whether you are looking for nourishment or supplies for the next home improvement project, Grape Nuts (aka pea gravel) delivers. Combined with milk, Grape Nuts competes with industrial concrete after approx. 5 minutes. Budding engineers can be seen building replicas of the Aswan high dam in their bowls, holding back a huge reservoir of milk on which to water ski, etc. This is followed by the obligatory "disaster" where the dam breaks and the milk spills in to kill all the poor farmers who were displaced by the dam's construction.
Needless to say, Grape Nuts can be a great source of energy in the morning, and if you can't finish them all, they make a great spackle for the bathroom.
You simply can't beat Grape Nuts for weight/volume ratio. I tried to sneak out a backpack full in college and just barely made it out of the dining hall before the straps ripped out.