Ben's answer above is good. I wish I could give him more than just one upclick.
Rules of thumb:
Carbs and proteins run 3.5 to 4 calories per gram. Fats run aobut 9 calories per gram.
Working hard, especially in cold weather, you can tolerate a lot of fat in your diet.
When planning food for teenagers, I figured on 4000 calories per day.
This is sufficient for days with 8-9 working hours per day. (Pretty hard core compared to most recreational use.)
With a 40% fat content diet, each hundred grams of food with provide 40 * 9 + 60 * 4 = 360 + 240 = 600 calories. So it would take 700 grams of food per day -- about a pound and a half. Our meals tended to be lower fat than that, and a rough rule of thumb was 2 lbs dry weight per person per day.
Two pounds per day means that the groceries for a 15 day trip are 30 lbs. With the high fat option (LOTS of nuts, lots of cooking oil) There really isn't getting around that.
So, as others have pointed out, you need to make the rest of your gear light, and minimize the parasitic weight (packageing) of your food.
If you do trips frequently, set up your food in a spread sheet. I had one in which I figured on the weight/volume per serving, had a constant for the number of people in the trip, another constant for the class of trip, and the spread sheet would figure out the packing weight/volume for everything. This makes things a BUNCH easier when packing for an expedition of 30 people for 3 weeks in the wild waters of northern Saskatchewan.
One aside: An external frame pack is considerably easier when handling lots of weight. They tend to be wider and flater, so keep the load closer to your own center of mass. They are however a true PITA in brushy country, as the extra width and exposed corners catch.
Weight i not the only concern - bulk comes into it when packing for 14 days. You need compact, high energy foods. Focus on High fat, high protein. Its easy to overload on carbs as dried, light food is almost always carb based. Too high ratio of carb will leave you feeling hungry even if you have eaten enough. – mattnz – 2015-03-23T20:45:26.737
Relevant XKCD What-If? Turns out butter is the most dense calorie/pound food.
– Doresoom – 2015-04-20T16:51:35.61725
and don't care about eating the same tasteless thing every day if necessary
<-- This makes me sad. If you are suffering, you are doing it wrong ;) - when you have your tent set, your pot on the stove, and watching the sunset, who wants tasteless? You want a symphony of flavor with that back-drop. Delicious doesn't have to be heavy. – Lost – 2012-01-25T02:03:19.0832I would argue that for a 12-15 day hiking trip you wouldn't need to fulfill all your food needs anyway - just stock up on enough calories to sustain you through the day. You don't need a healthy and balanced diet for the trip. – Noam Gal – 2012-01-24T20:54:07.913
+1 for Sarek. Been there on a 12 day trek and it was amazing. Also tough. :) – fgysin – 2015-08-11T10:20:04.080
2
This questions is closely related to a-list-of-suitable-foods-for-a-long-hike
– Eyal – 2012-06-18T10:03:07.07334After walking 25km in a day everything tastes gourmet :) – victoriah – 2012-01-25T09:00:22.437
That's kind of what I mean by "food needs": just enough to feel fine at the end of the day, it's not necessary to eat enough fibre or vitamins or whatever. – victoriah – 2012-01-24T20:55:03.917
1On one canoeing trip, we took a few summer sausages. An inch-thick slice will keep you going quite a while, and they aren't likely to go bad. – Kevin – 2012-01-24T20:58:32.790
I have read somewhere that people who go clim the Himalaya like to eat M&M's Mars and dehydrated soups. But I guess you can also go with Hardtack. – Vulpo – 2016-05-26T08:14:00.817
peanut butter has a good calorie density (6cal/g), keeps well, packages easily, contains carbs, fat and protein, no sugar, tastes good, and can be eaten from the pot with a spoon. – njzk2 – 2016-09-27T19:38:21.597
@victoriah 25km in a day :o are you superwomen ? – roottraveller – 2017-02-22T09:24:48.437
1@rootTraveller Haha no, i'm actually a super out of shape fat lazy woman. But walking long distances is pretty easy if you put your mind to it. It's just the uphill parts that are hard. – victoriah – 2017-02-22T09:26:28.710
@victoriah I will try my best to inspire from you :) – roottraveller – 2017-02-22T12:12:01.257