If you are lucky and live in certain areas of the country, some grocery stores will double or even triple manufacturers' coupons. This is where the grocery store will match (usually with some limits) the price listed on the coupon offered by manufacturers. Times and days when double coupons are offered vary from store to store, so check with your local store for days that they offer them. (sidenote: why some coupons have “do not double” printed on them)
You should also make sure that the coupon you want to use does not say “Do Not Double” on it as this will most likely exclude it from the grocery store's offer. Some stores will require you to join their store member program and you'll have to present the program card before the coupons will doubled.
Using double coupon days in conjunction with sale items can greatly reduce the amount you pay for groceries. Here is a list of some grocery stores around the country that have double coupon programs. If you know of others not on this list, please email me or leave a message below and I will add it to the list.