When a store has a sale and that item is out of stock you are usually entitled to a raincheck which will allow you to purchase the that item when it is re-stocked at the sale price.
This can be a great adantage for coupon shoppers as this will allow you to find, trade, or order from a coupon clipping service additional coupons so that you can stockpile that item.
Savvy coupon shoppers know that the store does not need to be out of stock of all the varieties offered in the sale flyer but instead look for just one flavor or type to be sold out and request a raincheck from the cashier or customer service desk. So for example if Pepsi 2-liters are on sale this week for $0.79 each, but the store is out of stock on just the Wild Cherry flavor you can ask for a raincheck because the store is out of stock. Usually they will write you a raincheck for any flavor, although sometimes they will indicate that you can only purchase the flavor that is out of stock.
Unless there is wording on the store sale flyer that indicates that the sale is limited to stock on hand or other such wording then by law in most states the store must issue a raincheck if they are out of stock or offer the consumer a substitute product. So extend your buying time by looking for out of stock items in the grocery store that are on sale and ask for a raincheck. Some rainchecks never expire while others, depending on the store policy expire within 30 days. This is plenty of time to aquire more coupons and stock up!