Before I got my fridge, I used dry ice all the time.
First and foremost, you never use dry ice to keep food/drinks cold.....Ever. Dry ice is about -109 degrees. Ice melts at 32 degrees. say goodbye to your food if you do (ask me how I know this).
I would pack my ice chest with ice, food and drinks. In my other ice chest I added 10 pound blocks of ice and dry ice. By the time my normal ice was done, the dry ice was gone and the blocks had warmed up to around zero. Break the blocks up and add to chest as needed.
Longevity wise, the dry ice would last about two days. I would get 4-5 days out of my ice depending on outside temp.
