Storing an 'In Case of Emergency' contact along with a name and telephone number will enable emergency services to quickly contact someone for you in the event of an emergency.
Eight out of ten people in the UK don't carry next of kin details yet 80% carry a mobile phone, most of whom have it with them all the time. There is no simpler way of letting the emergency services know who to contact should you be involved in an accident than by using ICE.