1) A jar of peanut butter. A few bites really go a long ways. Quite filling, since it has a good balance of protein, carbs, and fats. I used to have a difficult time eating peanut butter without something like jelly or jam, but I'm quite used to it. My main rule is to make sure I have a drink ready to go. I don't like stopping for long, so when I do, I tend to scarf it down. Peanut butter doesn't like to be scarfed.
2) Granola bars or cereal bars. Not quite as beneficial as peanut butter, but pretty good for easy food.
3) 1 gallon of liquid. Usually, 1 quart of tea, 1 quart of Gatorade, and 2 quarts of water. I reuse the 1 quart sized Gatorade bottles. I have a couple of springs that I'm not scared to drink out of, so when I'm going there, I don't take as much.
If there is a chance I might end up spending the night in the woods, I'll take extra dry Gatorade in Ziploc bags, extra granola bars, and I'll make sure that the jar of peanut butter was full before I left.
Sometimes, I'll take something like Honey Nut Cheerios to mix in with my peanut butter. I am trying to tell my brain that it is something completely different, but I think it knows better.
On occasion, I do take Vienna sausages, but then I have to take extras. I like them more than the peanut butter, but they just don't satisfy my hunger.