It seems like most of the methods out there for icing an injury aren't actually ice. There are countless sizes and consistencies of gelatin packs, fancy fabric-covered slabs of silicone rubber and the good old bag of frozen peas. But as far as I know, you can't get any one of these products by pushing a button on your refrigerator door. That would be ice.
When ice melts, you don't put it back in the freezer. You don't have to buy two or three bags of it and rotate them out as they lose their cool. You pour it down the drain and you get more. And there are plenty of ice packs out there. You can get an old-timey round rubber pouch like Wile E. Coyote always had on hand, or you can just use a ziplock baggie. But those classic ice packs have small openings and a small footprint, and Ziploc baggies leak.
Instead, use something that doesn't leak, has a large opening and you don't need cartoon magic to pull out of thin air; your hydration pack bladder. They're incredibly durable, easy to shape around whatever needs icing, and you've probably got at least one within limping distance. And the best part is, as the ice melts, you can drink it! Hydrating helps the healing process, and it's way healthier than drowning your sorrows after an injury.