lower drinking age
if you can drive at 17 and join the army at 18, you should be mature enough to drink at 18. also, if it's allowed, it would be less tempting and it wouldn't be abused.

end world hunger
if there were pipes that went directly to poor people worldwide, when people say, "you have to finish that! there are starving peope in africa," you don't actually have to finish it because someone who needs it would get it right away.