IMO one of the most important things to have 2+ of, if not the most important, is a flashlight. I try to be something of a minimalist with my EDC, though, and for me, the light from my cell phone is sufficient for a backup. I know, some of you may scoff at that. For me, a light and a writing utensil are the two EDC items that can quit without warning, so those are top on the list for me. The phone also serves as a backup for my Fisher Space pen because I can record notes in it. Of course a knife is also very important, but at least it won't quit suddenly and even if it becomes dull, there's a chance you can still use it (although it won't cut as well) or even find a way to sharpen it.