In a survival situation, you won't make it very long without a sustainable source of calories. Stockpiled MREs and dehydrated meals are great for the short-term, and can be supplemented by what you're able to obtain from hunting, fishing, or scavenging. But for long-term situations, you'll need to think more like our ancestors from native cultures around the world. Rather than just eating whatever you can find before it spoils, it's beneficial to process raw substances into shelf-stable ingredients for recipes — flour is a prime example.
Flour can be made by pulverizing countless forms of starch — generally it's dependent on whatever wild edible thrives in the region. In the west, we mostly use wheat flour; Eastern and central Europeans often use rye flour; corn flour has been an essential element of South American cuisine for thousands of years. Rice flour and nut flours are becoming more common, but they're still just the tip of the iceberg — you can also make it from beans, bananas, cattails, mesquite pods, acorns, coconut, and much more.
In the latest video from Primitive Technology, the host shows how he produced flour from Polynesian arrowroot gathered from the forest in his home country of Australia. Kudzu — an invasive species that has spread throughout the southeastern United States — is another name for Japanese arrowroot, and can be used in a similar manner.
The rhizomes are dug up, washed, grated into water, repeatedly rinsed and drained, and dried over a fire. This arrowroot flour can then be rehydrated to make bread or pancakes. Check out the full video below: