Accounting question please help

Megagrocer is a grocery chain that operates five stores. The stores are supplied with produce, meat, dairy, and dry goods by six separate vendors. In addition to the stores, Megagrocer maintains an ecommerce site through which customers can order and pay for groceries. The groceries are packed and delivered to customers from one of the five stores in a Megagrocer vehicle (van) by that store鈥檚 personnel. Think about the accounting information systems that Megagrocer might use.

What types of source documents might be collected by the Megagrocer to be processed by its accounting information systems?

Why are those documents important?

Source documents (and importance) - purchase orders from Megagrocer to its 6 vendors (to prove what it ordered), delivery docket from its vendor with its receiving supervisor's acknowledgement (to prove what was received), subsequent invoice from the vendors (to bill for what was delivered), payment vouchers approved at the right level (to pay vendors' invoices and to ensure proper approval), purchase orders or order forms from customers (to prove what the customer ordered), delivery dockets from each of the 5 outlets accompanying goods delivered containing customer's acknowledging signature (to prove he did receive the goods), the cashier's till roll from the cash register (to record each day's takings from each of the 5 outlets), etc

The e-commerce would not generate any source documents unless you print out the orders. Overall, the a/cg information system used by Megagrocer should be able to capture all the purchasing and sales transactions (providing enough details of vendors and outlets), and all the receipts and payments transactions, whether over the cashier's check-out station or thru e-commerce. Preferably it should be sophisticated enough to generate sales, COGS, and gross profit of each outlet. This would allow comparison by management of the outlets' gross profit margin. If there's any drastic difference reported by any outlet, it should be investigated for theft, whether by shoplifters or staff.