-Jump pack. Has saved others far more than me, but still great to have.
-Work specific: extra scrubs, socks, and old tennis. Nothing like spending a day with shit in your socks and shoes to train that habit! (ahhhhhhh the majestic career of nursing!)
-Truck specific: keep some of our barebones camp gear, like a stove. This came in handy when I got stuck from a freak blizzard a few years back. Could I have survived on cold chili? Certainly. Was this way more pleasant? YES.
-Bandaids in my wallet. Take up no room or weight basically, but people always manage to mangle themselves around me. Nice to have on hand (so to speak, heh)
-First aid kit (and more importantly, the knowledge to use it). See the aforementioned people's luck near me. It has come in handy on more than one car crash I've driven up on. Not to the 'save a life' degree, but hey, if I can minimize someone's blood loss and the amount of time they're freaking out, I've done some good in the world.
-Super easily digestible candy (smarties are my go-to). Learn to recognize the signs of hypoglycemia guys. More common that you might think. Especially if you're around a college campus and people have been drinking all day.
I keep extra windshield wiper blades in my car (along with the usual emergency gear). (What's that? Why yes, I DO live in the Pacific Northwest. How ever did you guess? And yes, I did have to pull over once and change a floppy wiper blade. That, at least, I know how to do myself.)
That is fucking BRILLIANT and I will be co-opting that immediately. No idea how that never occured to me!