You might have rust issues when using a metal container, and how do you plan on sealing it up? My first PSK (it wasn't called a PSK back then, just "emergency stuff") was stored in a metal band aid container. It was probably about double the size of an altoid tin. The top was sealed with electrical tape to keep the contents dry, but that also prevented easy access to the contents. In a way, that was good because I wasn't tempted to steal the lighter out of it all the time when I couldn't find one. But it was bad because I didn't open it often enough to check on the contents. When I finally did open it after a few years, I found the inside just covered with rust, and most of my stuff ruined.

Moral of the story: Metal can rust, even if sealed and kept dry, and check your stuff often.

I think if you plan on carrying this in a backpack and size isn't an issue, I think there are better containers than a soup can. Those side cut can openers are great for opening cans, but even with those the lids don't really fit back on very well.
What about using a Nalgelene bottle, can you boil water in those? Or maybe a coffee can with a resealable lid?