How long does ice actually last in a cooler in real-world use?

Probably 2 to 5 days if you’re not opening it constantly. Marketing claims of “7–10 days” assume a full block of ice, a pre-chilled cooler, and no one peeking inside every hour. In 90°F weather with bagged ice and normal use, you’re looking at 2 days for a small cooler, maybe 4–5 for a big one. The real trick is pre-chilling and packing it full to minimize air space.