We used to eat this stuff (and the vegetarian counterparts) while backpacking in the 90's. If you're putting on high mileage, you end up consuming 5000+ calories per day. Pemmican is one of those things that your body learns to love. The first time you taste it, though... and some folks never get used to it. There's probably a whole generation of Philmont boy scouts with horror stories to tell about pemmican bars.

Once my group went super high mileage, we just took tea, rice, vitamins (electrolyte powder wasn't popular yet), and iodine for water treatment. It's amazing how far you can go in a couple of weeks if you're willing to wear river-washed clothes, eat flavorless food, and lose 10-15 pounds in a go.

I'd always carry a can or two of spam, though. Ten or twelve days in, the guy with the salty canned "meat" is a bonefide hero.