To stay safe, sandwiches, salads, and other meals with perishable ingredients shouldn't be left at room temperature for more than 2 hours—max. Leftovers should also go back in the refrigerator within 2 hours.
It is recommended to keep the dry ice at the bottom of your cooler. Due to its extremely low temperature, dry ice will freeze the food it comes into direct contact with. Adding an extra layer between dry ice and food products, like cardboard, newspaper, or a cloth layer, will help keep your food cold, not frozen.
Q: Can I save dry ice in my freezer? A: No. Dry ice turns to a gas at –109.3° F, so even a freezer will be far too warm to prevent that from happening. And dry ice should never be kept in a walk-in freezer, because it produces carbon dioxide that can be hazardous in poorly ventilated areas.