Leftover rice is the most useful thing in the fridge and the most commonly thrown away. Cold rice behaves differently from fresh rice, and almost every good use depends on that difference.
Cool it fast and use it within a day
This is the one rule worth taking seriously. Cooked rice can harbour bacteria that survive reheating, and the risk comes from leaving it at room temperature for hours, not from keeping it. Spread it out to cool quickly, refrigerate within an hour, use within a day, and reheat until it is steaming hot all the way through.
Fried rice needs yesterday’s rice, not today’s
Fresh rice is too wet and clumps into paste. Cold rice has dried out and the grains separate, which is exactly what frying needs. Hot pan, a little oil, whatever vegetables you have, push them aside, scramble an egg in the space, then the rice, then soy sauce. Six minutes.
Rice soup and rice pudding take the softest rice
If the rice has gone hard and dry, simmer it in stock with anything else in the fridge until it collapses into a thick soup. In many cuisines this is a dish in its own right, not a rescue. The sweet version is the same technique with milk, sugar and cinnamon. Both work better with old rice than fresh.
Rice cakes and stuffed vegetables use up small amounts
Half a cup of rice plus an egg and whatever cheese or herbs are around makes patties you fry for three minutes a side. Or mix it with anything chopped and bake it inside a pepper, a courgette or a tomato. This is the best use for a quantity too small to be a portion.
Cool it quickly, keep it one day, and treat it as an ingredient rather than a leftover. Yesterday’s rice is better than today’s for almost everything except eating plain.