What knowledge do you think might save the life of a person someday?
I think every child should be taught basic first aid at school and go on refresher courses every 5 years. In the UK, St Johns Ambulance service is an excellent charitable NGO that attends events and runs first aid courses and also run such a scheme to teach and refresh first aid training. You even get a certificate!
As for specific knowledge, I think things like giving an aspirin to someone having a heart attack, or knowing the basic recovery position are very worthwhile skills to know, as the famous Heimlich maneuver which is a quite straight forward procedure to dislodge something stuck in a persons throat, like food when someone is choking for example.
Another very useful thing to know is what to do in the case of burns, where you must run the affected area under cool water as soon as possible, before covering with a sterile dressing.
However, the mostmimportant thing to know is how to get proper help. The numbers to call for emergency services or in the case of the UK, the NHS 111 helpline.
Don't forget that although Google is good, it and you are not doctors so never take a risk and call the professionals if you are in any doubt about the severity. If action needs to be taken before help gets there, they are the ones who can give you all the help and advice you need over the phone.
Common sense always saves the day!
http://www.sja.org.uk/sja/default.aspx