“cans of tuna spoil eventually...”
Not for many, many years. Taste may go off a bit, but unless you got a broken seal or botulism, canned food stays edible for decades.
A couple months ago I popped open a can of tuna with BB date of 2013. Made some tuna salad sandwiches. They were fine.
“Not for many, many years. Taste may go off a bit, but unless you got a broken seal or botulism, canned food stays edible for decades.”
Not true. 3-5 years is safe. Maybe a little longer for frozen. Eating decades old canned meats is very risky. Definitely not a good game plan when there are options to use ahead of time.
Carbs and proteins are the forms of calories that store well long-term (decades ranges). Need to remove oxygen and control temperatures. You can also get calories from alcohol which is like carbs. Alcohol stores very well.
Fats and oils go rancid over time no matter how you store them. Partially hydrogenated oils (like Crisco) aren’t good for you but do have a long shelf life, so that’s a reasonable compromise when facing life-threatening famine.