Honestly, I learned to make Overnight Oats from my daughter and there are NO rules. I've used Quick and Old Fashioned Oats (Old Fashioned is better but in a pinch...) and I usually just put in milk, brown sugar, berries and in the morning, I sprinkle it with pecans:) YUM. The milk soaks into the oats and you don't have to heat anything, just eat it cold with a steaming cup of coffee and it's amazing. And kids LOVE it.
If you want to get a little fancier...and probably a lot healthier...follow one of the recipes below...