I've once managed to 'roll' a can open. Rolling the top edge at an angle until it starts bending somewhat. You wear down the seal like that, then you smack it real hard against something and can get it to pop open.

Also, if anyone is sentimental and is still carrying any of their keys from before SHTF, you can open a can with keys.

I personally travel with a small can opener and usually a couple cans of something or another to eat. For emergencies (if I get stranded somewhere, I'm not likely to leave the safety of my vehicle unless it's a sure bet I'll be alright) and also when traveling long distance it's nice to have some simple canned goods to make in hotel room microwaves. (If the hotel room doesn't have a microwave, they usually still have a small coffee maker, which is also really good for cooking canned foods or most instant foods that only require water, like ramen.)