- Grappling hook is nice and useful (if it works as well as Rorschach's, and other vigilantes', does.
- Bullet-proof vest (few can be Ozymandias and catch bullets).
- Wristbands with several uses, like spraying paralyzing/neutralizing gas, short-range laser, keep small tools for breaking into places and cutting free from bad situations, an uncrackable self-destruct option (take them by surprise without getting it used against you!), a watch (what? I want to know the time a lot of times!), and if I could push it so far, also be a Web Launcher (epic way of disarming people or immobilizing them them).
- A towel (must never forget to carry one with you!)
- Night-vision goggles (you're not an owl or guided by sonar radar, I assume).
- Pen-knife is an excellent idea!
- Another stretch: Captain America's shield (with the function that it goes back to you after it's finished wrecking havoc; plus, I don't think there's a law against carrying a shield).
If I must choose one: The wristbands for its many uses, bullet-proof vest in second place and grappling hook in third. (sorry, but I don't trust the towel that much)