We have been doing this for the last five years, have never had to go to Camp Arctica, and here is how it has been: For four of us per RV (if you are in tents, subtract two or three days from this), one 130-gallon ice chest with five seven-pound bags of ice on the bottom, 30 pounds of dry ice in the middle, and three 20-pound bags of ice on top will keep for six days on the playa if kept in the shade and modestly insulated. So multiply that by two for eight of you. Also have an icechest already filled with your too-be-consumed drinks and fill that with regular ice. Freeze any OJ and jugs of water you can (those that won't be drank for at least three days) and they can keep other perishables cool. If you are tenting it, bring along duct tape and tape the lids of your dryice container shut. This will add another 48 hours to its overall usefulness. Now if you have to go to Arctica, make sure without fail you have an icechest to carry your bags of ice back to camp in (they melt unbelieveably fast, or so I have been told) and if you're more than a mile away, some kind of insulation. I hope this helps.
Doc, Barbie Death Camp & Wine Bistro