Activated charcoal can remove some toxins if the water source is iffy. It would still need to be boiled afterwards.
And never leave ANY flame unattended.
Surströmming is sold in cans, and while I suppose it’s technically edible, I’m not sure I’d recommend it. It’s filleted herring which is salted just enough to stop it from rotting and then allowed to ferment in the can, which causes the can to pressurize and bulge.
I bought a can off eBay once out of curiosity, took it to the park to open it, and ate it the way the Swedes do - in a flatbread wrap with sour cream, chopped onion, boiled potato, and dill, with a shot of vodka on the side. The stench is INTENSE, like a combination of sulfur, tequila, and old socks. My thoughts afterward were “That wasn’t as bad as I expected it to be” and “Now that I’ve done that, I never have to do it again”.
WRT water, we briefly considered one of these: it’s essentially a giant Lifestraw, no electricity needed, suitable for families or even entire neighborhoods if you take turns doing the hard manual labor needed to produce lots of potable water from dirty water.
We decided against it for now, because it’s bulky and we don’t want to store it, it’s a lot of money for something we most likely will never need, and while we have a river running through our property so definitely have a water source, the river is downslope about 150 feet, so the Lifestraw isn’t going to help us unless we’re feeling spry enough to haul water uphill. (Which we are, but in 5 years? Maybe not.)
If things really go south, we may reconsider and get one.
I have one of the Sawyer 1-gallon gravity bladders for camping or emergency. Essentially a Capri Sun-like Tetra Brik so a lot less to haul. Looks like it’s not as fine of a micron, but on the other hand 4 extra bladders is $75 or less instead of $330.
If you were using that for real, I bet you’d want to pre-filter the water with a fine sieve or maybe a tightly woven piece of cloth, so the filter doesn’t get clogged with random crap.
Of possible interest re: the water filtration issue: the Project Farm guy just tested a bunch of home water filters. He notes that many of them advertise that they are “certified” to remove “[insert various nasty stuff]” but most don’t do squat.
But there are some that work well.
Impressive! We’ll test that! I enjoy the Project Farm guy.
As far as the OP’s question, unless the canned food has been condensed so much it may be harmful (salt levels?), which it would probably be termed more as an additive I can’t hink of any thing. Maybe gross to eat but wouldn’t kill you.