Sometimes I'm camping and my food is in a can but I am without a can opener. How do I neatly open the can? Bashing it with a rock is futile.
I ran across this video some time ago, and I feel it is relevant to this question. If you have absolutely nothing but you can find a flat rock, you can get the can open by rubbing the top against the rock and abrading / sanding away the seal on top of the can: https://www.youtube.com/watch?v=XG-yZT3VH0M
I hope you're not camping without a knife. A sturdy knife can be used to slice the top off. Be careful of the edges!
If you don't have a knife or anything else sharp your options are limited. Your best bet might be to find a pointy rock, and bash it into the top of the can with another rock, gradually 'chiseling' out the top of the can.
But if you've managed to get yourself into this situation, how are you camping somewhere with power and a data-connection but no knife? May I suggest a new hobby?
Camping without two can openers is like clapping with one hand. As Tom mentions in his answer, you can use a knife like a can opener. Poke the knife through the top of the can, and rock it back against the rim of the can, go around just like a can opener.
Of course if you are looking this answer up online, at the time of need, forget the can and order a pizza.
The best solution is prevention. The P38 can opener can be purchased for less than one US dollar, buy a bunch of them and put them in your car, on your keyring, and a couple in your camping gear.