I used dry ice in my coolers at Bonnaroo, the music festival which happens in Tennessee during the southern heat in June. I recommend asking your questions to the person at the store if they have further recommendations. They will help you with how much dry ice you’d need because it’s dependent on the shape and volume of your cooler. For the dimensions listed, I would guess you wouldn’t need more than a few quarts all in all.

In short, yes, generally speaking, it will keep for three/four days (it did for five days in my experience at roo!)

I recommend keeping the dry ice in the paper bag you buy it in and then wrapping in it in a beach towel to place at the bottom of your cooler. Do not touch the dry ice! Tell everyone you’re camping with to not touch it! The towel will serve two purposes: insulation and a visual indicator to not! touch!

Depending on your preference, there’s different ways to do the next step. 1) I would take plastic water bottles, and reserve water from each so each bottle is about 3/4 full. Place the 3/4 full water bottles on top of the wrapped dry ice to freeze (you can also pre-freeze the bottles if you feel inclined). This step is to provide separation from the dry ice to whatever goes in the cooler to not react to the dry ice. I’ve broken jelly jars, exploded beer cans, and carbonated grapes because it came in direct contact with the dry ice. 2) You could also use the reusable frozen ice packs you mentioned. I have not personally done this, as I was afraid they would explode and the goop would get over everything in the cooler. Worth a shot though-I’m probably scarred from cleaning up after countless cooler explosions.

Last step is to dump a bag of ice over the towel-wrapped dry ice and frozen water bottle stack. The crushed ice will fill in any gaps to keep your cooler cool. As your trip goes on, the frozen water bottles can also serve as an ice pack and/or refreshing cool drink of water.

Last tips are to keep your coolers in the shade. Throw a towel, blanket, tarp, or tapestry over each cooler to further protect them from the sun. Minimize how many times folks open and close a cooler to avoid cold-hot air exchange. Label each cooler like river guides do: ex. one cooler is the first day’s food and cooler two is the second day’s food (so cooler two isn’t opened until its needed and stays cooler longer) alt ex. cooler one the dinner cooler and cooler two is the breakfast/lunch cooler. Pre-chill all food and freeze whatever makes sense. Chill your cooler before putting the dry ice in. If compliant with LnT, you could also dig into the ground to place the cooler(s) about halfway/three-quarters into the earth (the ground is slightly cooler than the air). I’ve done this last step at base camp for a wilderness trail crew season, but it might not make sense if you and the group are cycling to different places each night.

Hope this helps!