I saw this video on YouTube that shows an ingenious way to open canned goods when you do not have a can opener.
This could be important to know in a survival situation. The technique uses a concrete sidewalk or very flat rock to file off the crimped ridge on the top of a can, which makes it easy to pop the top off the can. In many cases, it works faster than using a can opener.
A sheath knife can also be used to open a can if you use it to punch through the top of the can near the crimped ridge. If you keep both of these techniques in mind, you will never starve for lack of a can opener.