Do the classic rock salt experiment of dissolving, filtering and evaporating. Also note the effect of adding salt to ice, melting it to water and dropping the temperature. For surprising results, freeze homemade salty water then lick the ice cube.
Demonstrate the basics of chemistry by showing the poisonous gas chlorine combining with violently reactive sodium to make salt.
Demonstrate electrolysis of salt and lead into industrial methods - especially newer "greener" chemistry - used to obtain some key bulk chemicals. Research all the marvellous uses of sodium, chlorine, hydrogen and sodium hydroxide.