In the past, we've mentioned the importance of improvised weapons. Even if you're always armed, you could easily get robbed and end up in the middle of nowhere with only the clothes on your back. Knowledge weighs nothing, so it's wise to learn other ways to create handmade weapons and tools for when SHTF. Even if you never have to use this knowledge, it doesn't hurt to learn.
One of the best ways to create knives and tools in the wild is through a technique called flint knapping. If you've ever seen an ancient arrow head or spear, you've probably seen the results of flint knapping. The technique uses a brittle stone and a hard striker to chip away razor-sharp and thin fragments. These fragments can then be chipped more to form tools.
Note: Always wear eye protection when flint knapping, unless you want tiny razor-sharp bits of stone in your eyes. Gloves are also a good idea to prevent nicks and cuts.
This video from Paleoman52 on YouTube shows the steps involved. One thing the video doesn't mention is the type of stone to use, such as flint, chert, and obsidian (all of which can be bought online for practicing). If you're looking for stones in the outdoors, try tapping them and listening to the pitch—higher pitch is usually better for knapping.
For more information on flint knapping, check out this guide from WildernessCollege.com.