I carry a small squeeze bottle of olive oil and add a squeeze or two to the food before adding the hot water. At about 1,000 calories for an ounce of weight (approx. 9 tbsp per ounce) it's very calorie dense. Otherwise as others have said Snickers or gorp add a lot of calories as does Trader Joe's ...

Here's a useful vidoe: http://www.youtube.com/watch?v=_J4D3AHzlxQ
Backpacker mag article with an AT gear list including clothing system: http://www.backpacker.com/november_08_pack_man_/articles/12659?page=4

I'll add a disclaimer that I hike warm and am fine with a thin wool skullcap, a midweight ...