Elephants love plant based foods. One of their absolute favorite foods is grass. The simple food is one of the easiest things to find on the savanna plains where they live. Since Africa is rather barren where they live, this is one of the easiest ways to find food - just eat what you’re walking over. They also like tree bark. When they can find trees - it happens more often than you’d think in the plains of Africa - they will eat the bark that has fallen off the tree, as well as use their trunks to get more off.
All of this pales in comparison to how much water they can drink, but that’s beside the point. Water is also one of their favorite foods, mainly because they need water to live. Like every other living thing on the earth.