Vinegar has preservative properties and can be used not just to make rice last longer, but in many other types of cooking too. It also helps to prevent summer fatigue so I really recommend it.
I learnt this trick from my mother.
All you have to do is cook the rice as you would normally, but with a little vinegar. You won't even notice the scent of the vinegar once the rice has finished cooking.
Enjoy Japanese food around the world.