We often discuss the importance of having an easy to grab emergency kit prepared for the necessities of surviving without help for a few days. Earthquakes and Tsunamis have been the big disasters of note over the past few years, and both provide a very limited time frame to get what you need and escape. The Art of Manliness has taken this need of an easy to grab kit, but placed their kit inside of a shotgun instead of a bag.
The kit, as explained in detail here, addresses five core survival needs: water, fire, shelter, signaling, food. Beyond the obvious benefits of having a shotgun for hunting, shotguns typically have a lot of unused space to provide cushion for the kickback and can use special shells that act as signal flares. They mounted a knife, flashlight, various shells, parachute cord (that can be disassembled into several strands), a saw blade, bandana and compass on the outside. In the unused spaces they were able to fit a multi-tool, fire starter kits, and a rather comprehensive survival kit (containing items such as a fishing kit, aluminum baking-pan, water purification tablets, first aid basics, and a survival blanket). They claim it is the ultimate kit for a zombie apocalypse, however I can see a lot of benefits for more practical uses like getting stranded in the mountains.