I couldn't agree more.
AND a cell phone (sorry, LW).
(To all hikers) Think about others when you're out there. Carry not only what you think will help you, but what might help others (cookies, brownies extra chocolate pudding, too)!
I saw a long term hiker give his flashlight to a lost dayhiker in the White Mountains so he and his buddy could get back to their car. Pretty selfless. He figured he could replace it at the next road crossing (this was before headlamps were common on the trail).