Coconuts are one of those divisive foods that people tend to love or hate, but if you ever get stranded in a tropical paradise, a coconut could just save your skin—even if you refuse to eat it. That's because the liquid inside of a coconut is both sterile and perhaps the best naturally-occuring version of IV fluid known to mankind. That means if you end up living out the premise of Lost or Gilligan's Island and one of your party becomes severely dehydrated, you could use a needle, plastic tubing and a coconut to provide them with the fluids they would need to survive.
Obviously going to a hospital and using real IV fluid is preferable, particularly since some doctors worry that long-term use of coconut water as IV fluid would result in a potassium overdose. But if you're stranded, it could mean the difference between life and death.