My first thought was oatmeal too. I'm talking rolled oats - the flat stuff. It can pack VERY dense, which helps with storage. It can be eaten cold or hot, wet or dry (though its tough to whistle with a mouth full of dry oats).

You can buy it in 40 lb bags at feed stores.

If you are going the Cap'n Crunch route, make sure to get the one with Crunch Berries since fruit is a good part of a balanced breakfast. :-)