Yes! Sonic sells bags of ice. Sonic Ice is the best ice you'll ever taste. You can buy whole bags of it. You'll find it in bags that are thick and have a very chewy texture, and unlike other ice, it doesn't seem to melt as fast. Nugget ice, also called chunk ice, is great for cooling down drinks and smoothies.
But it's not on the menu, so you need to be courageous enough to go up to a staff and ask. It will cost you $1.99 to get a single bag of them. But be careful, because they sell ice only in large bags that weigh 10 pounds. Make some room in your fridge!