I've played around with various EDC items for years, but 3 things I have almost never been without (and regretted it when I was):
1. Leatherman Micra (carried this even while carrying "test" replacements.
2. Fisher SpacePen (Lost a few over the years, now carry the titanium version with a fine tip replacement). It doesn't write as nicely as a Pilot G-2 or other Gel inks, but it ALWAYS writes.
3. Leatherman Multi-tool. I carried my Wave until I lost it, carried my New Wave until I opted for the Titanium with S30V blade. Regardless of your feelings on the version (usually centered on the driver bits), it's effectively the same multi and not one version has ever let me down despite daily use and frequent abuse.