Make the coupons be for a specific generic item: 2l 2% milk or 2lbs ground grade-A beef or 300g medium cheddar with no restrictions on brand name.

J random wanderer gets a deck of cards each month based on dependents and dietary needs.

Then guarantee a purchase of these coupons for the first supplier who can guarantee stock to redeem all coupons at that price, lowering the price by 1% every time 2 organizations submit RFQs.

And now we have single-buyer reverse monopoly for food like we do for public healthcare.