One of the most important elements of being prepared is owning a first aid kit. I always made sure mine was stocked and ready, so I'd be prepared for that moment when I might need it. The reason I'm talking about being a lifeguard and safety is to make sure you're prepared when you're out riding. If you don't, get one. It's important to know what to have in your kit and maybe what to leave out as well.
Most kits come with some form of antiseptic ointment.
While this is good for minor injuries, such as sunburns or scrapes, ointment should never, under any circumstances, be used for major injuries. Often, the best thing to have is filtered water. The water can be used to clean cuts, wash particles from eyes, and even maintain moisture in case of a broken bone. Another thing I always have in my emergency kit are several pairs of latex gloves. The gloves are always very good with regard to maintaining heat and the body's natural moisture on cold rides as well.