I've used the "Lose It!" app for, well, losing it (body weight). It has long been recommended that to lose weight, you should log all the food you eat. Well, "there's an app for that" now. It works. And in addition to making me more conscious of how much that cookie or slice of pizza blows my daily budget, there is also a video-game, playing-to-win aspect of it in which I give myself strokes for a smaller portion or longer hike that "wins" by coming in under budget that day.
But back to the original question: there are thousands of store-bought foods in the database, including basic ingredients like olive oil, cornmeal, carrots, white enriched flour, rice flour, brown rice flour, all-purpose flour, etc. So you could calculate the calories of any recipe. I haven't used that function, but it will let you assemble custom foods and meals from its database or your own entries.
I see so many people on the trail, finishing every trip with so much extra food. If they tracked the calories packed per day and per mile) and adjusted accordingly, they could quickly fine-tune their packed food to have no extra. This whole "bring an extra day worth of food"?!? Who among us couldn't stand to lose a pound of fat?
That would another way to use that app because it calculates the calories consumed from (1) basal metabolism for your gender and body weight and (2) the additional calories consumed per hour of hiking (general / backpacking / mountain climbing) or walking (2, 2.5, 3, 3.5, 4, 4.5, 5 mph) although I wish they had an option of XX horizontal miles plus YY vertical feet with ZZ pounds on your back. As a first cut, you could plug your body+pack weight in as your body weight and 7 hour of 3 mpg walking for a 21-mile day and see how many calories you'd burn that day. You should pack that many calories for a long, thru hike, but for a hike of a week or two, you can be 500, 1000, even 2000 calories per day under your expenditures and lose a few pounds each week of your hike.
Dehydrating doesn't change the calories in the food, it just removes the water. So calculate the original food at its original weight, or use its dried weight and dried calories/weight.