A staple food for native americans in certain areas at certain times of year was cattail pollen, it was used sort of like a high protein flour. Cattails really are the ultimate temperate-climes survival plant... if you have cattails you have, depending on time of year, protein (pollen), carbs (roots), vitamins and mineral-rich greens (sprouts, core, developing flowers), water (they grow in freshwater), insulation (tufts), firestarter (tufts), fire holder (mature flowers), candle (mature flowers soaked in fat), thatch (leaves), fuel (dried stems / leaves)... usually even fish, too, they like to live among them. And one can commonly find grubs at the base of browned cattail leaves that one can use as bait.
The only other plant I can think of that could best it in terms of all around providing for one's survival is the coconut palm.