Don't forget that modern tents and modern bicycles and modern guns, etc. all require electricity and mass-manufacturing techniques to build parts keep things operational. At some point, the stockpile of modern tents and bikes and other such things would get worn out and broken, and there would be no good way to fix them.* Hence, the return to natural materials that can be fashioned with manual tools. *I realize it would take a lot longer than 15 years for all the bikes in the world to get broken beyond repair. But the point remains. Modern stuff would eventually break and would not be repairable without modern technology.