Spam was a treat to the grunts in Vietnam. Plus, the division I worked out of (the 25th Infantry Division) was stationed in Hawaii when not required to kill people somewhere else in the world. You probably know where Spam stands in the Hawaiian culinary pantheon.
I think the most universally hated can included in C-Rations was the one that contained the legend:
Ham and Lima Beans. If you liked ham and you liked lima beans that made it even worse. It should have read "Fat and Disgusting Mush". You couldn't give it away let alone trade it for something else. Just about all other items could be swapped for something else. You know two peanut butters for a fruit cocktail, like that.
And I never really liked the canned bread myself. But, the container made the best little field stove - because it was dry inside. Open it with a P-38, remove the bread and throw it away, punch holes with a church key, place a small bit of C4 on a rock, light it, and then place the bread can over it. Then heat whatever.
I talk about it a little here:
http://forums.egullet.org/index.php?showtopic=106787(I talk a LOT more about it in the memoir on which I work sporadically. This piece is heavily edited.)