Plain and simple.
Shopping cart (example: for 10 grocery items)
The grocery items should include name, category, price and quantity and the total amount due. Buttons should be included for adding an item, removing an item and marking purchased items. The cart should have a side file that keeps the list cached (saved for later use or modification).
Program flow as follows: Use a hash to parse the form, do action requested and update the side file, re-display the new cart
*Plain and simple