Oatmeal is infinitely adjustable, up or down, expanding and contracting with ingredients available or desired. It's also a fairly decent source of protein, for a grain, anyway. Almost as important though it is a good source of bulk and fiber - a backpack full of highly concentrated high calorie high fat trail foods are not always very kind to our digestive systems. Until recently anyway, it was also absolutely dirt cheap. I make a concession to quality and use "old fashioned" oats, they do take a few minutes of simmering but this is of no consequence particularly except a tiny bit of fuel.
I also prefer a good quality powdered whole milk like Peak or Nido, and dairy butter. Rounding it out with honey, maple syrup, or brown sugar and (of course) Cinnamon. The resulting glop is so much better than the chemically enhanced instant packets. Since I rarely if ever make Oatmeal at home, although something I always take on the trail, when I do I'm instantly transported, if only for a second, to backcountry campsites and rainy mornings on the trail, and swear my feet start to hurt. For all that, I've never found Oatmeal to be particularly a "stick to the ribs" kind of breakfast. It seems like it should be. I only wish someone would invent a decent tasting powdered egg. That's one technology that seems to have eluded scientists. Are laying hens allowable on the trail?