A portable electronic data storage/processing device, e.g., smart card maintains an account including benefit packages. Each benefit package includes multiple items with associated quantity information. A smart card includes an account benefits interface and a retailer interface, each interface using different security measures. New benefit packages are added to the smart card through the account benefit interface by a benefit provider. Benefits debit request lists including multiple items and associated quantities are submitted to the smart card through the retailer interface. The smart card is the trusted member and checks if all requested items in quantities requested can be debited. If all requests can be fulfilled, the smart card executes the debiting from the currently valid benefit package and returns a transaction success indication to the retailer. If any of the requests of the list cannot be met, the entire request list is rejected and no debiting occurs. Benefit quantity addition is not possible through the retailer interface. Transactions are performed as block transactions.