This is my first post so please forgive me if flax seed has been discussed to death. Anyway, I just happened to look at the nutrition info on some cold-milled flax seed and was surprised to see how many calories it had: 6 per gram, or about 170 per ounce.
That's about the same as pecans and pistachios, but flax seed is also a great source of protein (about 6 grams per ounce), fiber (about 6 grams per ounce), omega-3 and 6, lignins and lots of other essental things.
It's quite compact when it's been milled. It also has a nice nutty flavor and goes well with cold cereals as well as oatmeal and cream of wheat. Haven't tried it with granola, but I suspect it would taste just fine with it.
Compared with a Cliff Bar, it seems flax seed has more to offer backpackers except for carbs; it only has about half as much per ounce. I'm going to start adding it to my morning oatmeal when backpacking.
Two single servings of Quaker Oats instant and two ounces of flax seed should yield about 600 calories.