And speaking of SPAM.
As a youngster my family would often camp for a weekend to two weeks. Station wagon, a couple of coolers, a tent, fishing gear and be gone.
Many of our meals came from a can. This was before ingredients were listed, I think, or no one cared. Our staples were canned corned beef, don't read the label, whole canned chicken, don't read this one either, and the list goes on of the same type goodies. You could tell it was chicken, because the label says so.
But other than that I have no suggestions other than sardines, but most of them are questionable also.