Keys are a very effective weapon.
I carry tampons in my first-aid kits in the Jeep and in my Survival Bag. They are the perfect size to plug a bullet hole if you ever need to.
For those across the pond, I have seen them used to plug a leak in a boat. They don't last long, but long enough to get to shore.
You can also stick one up each nostril with the strings hanging out.
Doesn't serve any purpose, but it is hilarious.