Advice needed on dry ice

[Kent]

I have never used dry ice before and I was thinking of getting some to keep our minnows frozen for a three-day fishing trip. How much do I need to keep a couple dozen large (6 to 10 inches long) minnows frozen? How long will dry ice last in a small cooler? Do I need to leave the lid sligtly open to allow for venting? I know that one can get burnt if they touch it, but if anyone has any other information/advice they want to share it would be appreciated.
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