What can I eat in Minecraft?

All food items with their restorative values can be found at the minecraft wiki. In my opinion though, the easiest food items to obtain at the very beginning can be obtained by one of two ways:

  1. Killing cows, chickens, or pigs and cooking the meat in a furnace
  2. Finding the two varieties of mushrooms (brown and red) and making mushroom stew. Brown mushrooms can be found just about anywhere. Red are typically a bit more difficult to find, but both can be found fairly often on the surface.

The entire list of restorative values are here.

and you shouldn't die unless you are on hard because the minecraft wiki page on hunger states:

If you have 90%-100% food you will regain health slowly, but if you have 0% you will lose health instead. On easy the player's health would slowly drop to 5 hearts, 0.5 hearts on normal, and all the way to death on hard