how to store rice for 12 hours so it doesn't dry out
For eating rice cold, I find it best to cool it by rinsing with cold water as soon as it's cooked. Then drain well, pack into a close fitting container, and refrigerate. It also works well if you plan to reheat the rice. 

You may find that you want it a little softer than at dinner the previous night. In that case let it sit hot and wet while you eat dinner, then drain before the cold rinse.

This rapid cooling, apart from preventing the rice from steaming in the box, is also good from the point of view of food safety.