Do any of you carry anything for emergencies?

I carry a whistle on every ride, hooked to my camel back's shoulder strap. I also use a "safeTband" this is a red band with a first-aid cross on it that I also put on the camel back's should strap. Inside it contains my blood type, info about what I'm allergic to... in my case Bees and people to contact if I'm injured.