We haven't had great luck with the buy groceries for your days scheme. It makes packing a pain, and we usually wind up with one spaghetti and hotdogs asshole who spent a third what most of the other groups spent.
We always split per person, and usually include shuttle, food, fuel to/from a selected destination where the majority of the gear is coming from. Most of us are from nearby anyway. It blows when 5 kayakers hop into a subaru and split their fuel, and two of us hop into a pickup with trailer and 4 rafts and have to split fuel.