How to split groceries fairly
Pool only the items everyone uses: oil, salt, spices, paper goods, dish soap, and perhaps coffee. Keep personal meals, special snacks, and expensive preferences separate unless the group agrees otherwise.
Use one simple record for shared purchases and settle it regularly. Split by equal share when use is roughly equal; adjust when one person is clearly buying for fewer people or using far less.
Do not make people chase small debts. A modest household fund can cover staples and reduce the number of individual reimbursement requests.