The fair way to split a shared grocery budget
Start with a short shared list: oil, spices, coffee, paper goods, cleaning supplies, and perhaps a few staples everyone uses. Divide that fund equally or by an agreed formula. Keep specialty food, alcohol, and expensive preferences personal.
Use a receipt and a shared list so no one has to remember who bought the last bag of rice. Set a spending limit for unplanned purchases.
If one roommate eats more, cooks more, or rarely participates, adjust the agreement rather than silently keeping score.