Muesli. But you need milk and/or yogurt, plus fruit, which does not always travel well. But if you pick up the ingredients you need...
In a bowl, soak rolled oats in milk or yogurt while you do the following:
Chop up fresh fruit.
Prepare handfuls of nuts, seeds, and dried fruit.
Stir everything together, and it's done. (10 minutes of soaking should be OK.)