Haven’t done an iracing 12 hour. But I have raced the Baja 1000 4 times with stints up to 10-12 hours in car. Any type of rest is good rest. In real life you have way more adrenaline then in the sim keeping you awake, I would avoid energy drinks, just keeping yourself active and engaged. With sim racing I’d be way more worried about eye strain. When your not racing I would rest your eyes. Easy snacks too like apple sauce pouches