My favorite is pemmican, a historical trail food made from meat, fat and dried fruit. Lasts quite awhile w/o out refrigeration, is really tasty and the calorie to weight ratio is really high.
There are many ways to make this - modify this recipe to suit your tastes.
1) Get a couple of lbs. of inexpensive lean beef - NOT ground meat though. Tough cuts are fine - you're only going to dry it and chop it up.
2) Cut the beef into small strips about the size of your little finger. Spread them out on a baker's rack or two, then put the racks on a baking sheet lined with tinfoil. This will catch any drips.
3) Set your oven to the lowest possible setting - mine is about 200 deg. F. Place meat in oven and leave the door open a bit. This will allow air to circulate. We're not trying to cook the meat as much as dry it thoroughly. Leave it in for 6-8 hours or until a strip breaks with a snap.
4) Put meat in batches into a food processor with a handful of dried fruit to taste (I use cherries, currants and/or raisins) Pulverize until the pieces are as small as you'd like, about 1/4 in. in my case.
5) Place the whole mess in a bowl and pour enough melted fat in to JUST COAT the mixture. You don't want a soupy mess, just enough fat to act as a binder as it cools. We're only talking about a couple of tablespoons here. If you don't have melted fat (see below), fresh bacon drippings or olive oil might work, but I've never tried. Don't use butter; it will go rancid QUICKLY.
6) Place in takeout containers or similar and chill until hardened.
A good pinch of this is about 300 calories and a lb of this has kept without problems for four days in August w/o refrigeration in my food bag - another reason to kept the melted fat to a minimum. It's basically jerky and dried fruit really.
I render my own suet and lard - comes in handy for various cooking purposes. Just get 5 lbs. of beef or pork trimmings from your butcher
(cheap or free - I pay .09 a lb.), cut into small cubes and cook overnight in your crockpot set on low. Next day, fish out the remaining unrendered meat and such, then strain melted fat through cheesecloth into large bowl. Pour lots of cold water into the bowl and stuff it in the fridge for several hours. The fat will float and solidify away from the water and and remaining solid particles. Break up the fat into chunks, wipe dry and store. Made with pork, this is the BEST shortening for bannock I have ever used. It may sound like a lot of work, but the yield is pretty good. Enjoy!